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Acute Coronary Syndromes (Heart Attack; Myocardial Infarction; Unstable Angina)


Ranya N. Sweis

, MD, MS, Northwestern University Feinberg School of Medicine;

Arif Jivan

, MD, PhD, Northwestern University Feinberg School of Medicine

Last full review/revision Jul 2020| Content last modified Jul 2020

Acute coronary syndromes result from a sudden blockage in a coronary artery. This blockage causes unstable angina or heart attack (myocardial infarction), depending on the location and amount of blockage. A heart attack is death of heart tissue due to lack of blood supply.

  • People who experience an acute coronary syndrome usually have chest pressure or ache, shortness of breath, and fatigue.
  • People who think they are experiencing an acute coronary syndrome should call for emergency help and then chew an aspirin tablet.
  • Doctors use electrocardiography and measure substances in the blood to determine whether a person is experiencing an acute coronary syndrome.
  • Treatment varies depending on the type of syndrome but usually includes attempts to increase blood flow to affected areas of the heart.

(See also Overview of Coronary Artery Disease.)

In the United States, more than 900,000 people have a heart attack or sudden cardiac death each year. And acute coronary syndromes cause almost 400,000 deaths each year. Almost all of them have underlying coronary artery disease and about two thirds of them are men.

Causes of Acute Coronary Syndromes

The heart muscle needs a constant supply of oxygen-rich blood. The coronary arteries, which branch off the aorta just after it leaves the heart, deliver this blood. An acute coronary syndrome occurs when a sudden blockage in a coronary artery greatly reduces or cuts off the blood supply to an area of the heart muscle (myocardium). The lack of blood supply to any tissue is termed ischemia. If the supply is greatly reduced or cut off for more than a few minutes, heart tissue dies. A heart attack, also termed myocardial infarction (MI), is death of heart tissue due to ischemia.

A blood clot is the most common cause of a blocked coronary artery (see also Overview of Coronary Artery Disease). Usually, the artery is already partially narrowed by a buildup of cholesterol and other fatty materials in the artery wall (atheroma). An atheroma may rupture or tear, which releases substances that make platelets stickier, encouraging clots to form. In about two thirds of people, the blood clot dissolves on its own, typically within a day or so. However, by this time, some heart damage has usually occurred.

Uncommonly, a heart attack results when a clot forms in the heart itself, breaks away, and lodges in a coronary artery. Another uncommon cause is a spasm of a coronary artery that stops blood flow. Spasms may be caused by drugs such as cocaine. Sometimes the cause is unknown.


Doctors classify acute coronary syndromes based on

  • The presence of substances in the blood (cardiac markers) released by the damaged heart
  • Symptoms
  • Electrocardiography (ECG) results

The classification is important because treatments differ depending on the specific acute coronary syndrome. The classification consists of unstable angina and two types of heart attack.

  • Unstable angina is a change in the pattern of angina symptoms (chest discomfort), including prolonged or worsening angina and new onset of severe angina symptoms. People who have unstable angina do not have signs of heart attack on their ECG or blood tests.
  • Non-ST-segment elevation MI is a heart attack that doctors can identify by blood tests but that does not produce typical changes (ST-segment elevation) on an ECG.
  • ST-segment elevation MI is a heart attack that doctors can identify by blood tests and also produces typical changes on an ECG (ST-segment elevation) .

Did You Know...

  • About one third of people who have a heart attack do not have chest pain.

Symptoms of Acute Coronary Syndromes

Symptoms of the acute coronary syndromes are similar, and it is usually impossible to distinguish the syndromes based on symptoms alone.

Symptoms of unstable angina are the same as those of angina pectoris—people typically have intermittent pressure, or an ache beneath the breastbone (sternum). People often interpret the sensation as discomfort or heaviness rather than pain. Discomfort also may occur in either shoulder or down the inside of either arm, through the back, and in the throat, jaw, or teeth. However, in people with unstable angina, the pattern changes. People experience more frequent or more severe episodes of angina, or episodes occur at rest or after less physical exertion. About two of three people who have heart attacks experience unstable angina, shortness of breath, or fatigue a few days or weeks beforehand. Such a change in the pattern of chest pain discomfort may culminate in a heart attack.

With a heart attack, the most recognizable symptom is usually pain in the middle of the chest that may spread to the back, jaw, or left arm. Less often, the pain spreads to the right arm. The pain may occur in one or more of these places and not in the chest at all. The pain of a heart attack is similar to the pain of angina but is generally more severe, lasts longer, and is not relieved by rest or nitroglycerin. Less often, pain is felt in the abdomen, where it may be mistaken for indigestion, especially because belching may bring partial or temporary relief. For unknown reasons, women often have different symptoms that are less likely to be accurately diagnosed as a heart problem.

About one third of people who have a heart attack do not have chest pain. Such people are more likely to be women, people who are not white, those who are older than 75, those who have heart failure or diabetes, and those who have had a stroke.

Other symptoms include a feeling of faintness or actually fainting, sudden heavy sweating, nausea, shortness of breath, and a heavy pounding of the heart (palpitations).

During a heart attack, a person may become restless, sweaty, and anxious and may experience a sense of impending doom. The lips, hands, or feet may turn slightly blue.

Older people may have unusual symptoms. In many, the most obvious symptom is breathlessness. Symptoms may resemble those of a stomach upset or a stroke. Older people may become disoriented. Nonetheless, about two thirds of older people have chest pain, as do younger people. Older people, especially women, often take longer than younger people to admit they are ill or to seek medical help.

Despite all the possible symptoms, as many as one of five people who have a heart attack have only mild symptoms or none at all. Such a silent heart attack may be recognized only when ECG is routinely done some time afterward.

During the early hours of a heart attack, heart murmurs and other abnormal heart sounds may be heard through a stethoscope.


People who have a heart attack may also have complications that can be long-lasting. The complications of acute coronary syndromes depend on how much of the heart muscle is damaged which is a direct result of where a coronary artery was blocked and how long this artery was blocked. If the blockage affects a large amount of heart muscle, the heart will not pump effectively and can become enlarged, possibly leading to heart failure. If the blockage shuts off blood flow to the electrical system of the heart, the heart rhythm may be affected, possibly leading to arrhythmia and sudden death (cardiac arrest).

Diagnosis of Acute Coronary Syndromes

  • Electrocardiography (ECG)
  • Blood tests

Whenever a man over age 35 or a woman over age 40 reports chest pain, doctors usually consider the possibility of an acute coronary syndrome. But several other conditions can cause similar pain: pneumonia, a blood clot in the lung (pulmonary embolism), pericarditis, a rib fracture, spasm of the esophagus, indigestion, or chest muscle tenderness after injury or exertion.

ECG and certain blood tests can usually confirm the diagnosis within a few hours.


ECG is the most important initial diagnostic procedure when doctors suspect an acute coronary syndrome. This procedure provides a graphic representation of the electrical current producing each heartbeat. In many instances, it immediately shows that a person is having a heart attack. Abnormalities detected by ECG help doctors determine the type of treatment needed. The abnormalities on ECG also help show where the heart muscle was damaged. If a person has had previous heart problems, which can alter the ECG, the most recent damage may be harder for doctors to detect. Such people should carry a small copy of their ECG in their wallets, so that if they have symptoms of an acute coronary syndrome, doctors can compare the previous ECG with the current ECG. If a few ECGs recorded over several hours are completely normal, doctors consider a heart attack unlikely.

Cardiac markers

Measuring levels of certain substances (called cardiac markers) in the blood also helps doctors diagnose acute coronary syndromes. These substances are normally found in heart muscle but are released into the blood only when heart muscle is damaged or dead. Most commonly measured are heart muscle proteins called troponin I and troponin T and an enzyme called CK-MB (creatinine kinase, myocardial band subunit). Levels in the blood are elevated within 6 hours of a heart attack and remain elevated for several days. Levels of cardiac markers are usually measured when the person is admitted to the hospital and at 6- to 12-hour intervals for the next 24 hours.

Other testing

When ECG and cardiac marker measurements do not provide enough information, echocardiography or radionuclide imaging may be done. Echocardiography may show reduced motion in part of the wall of the left ventricle (the heart chamber that pumps blood to the body). This finding suggests damage due to a heart attack.

Other tests may be done during or shortly after hospitalization. These tests are used to determine whether a person needs additional treatment or is likely to have more heart problems. For instance, a person may have to wear a Holter monitor, which records the heart’s electrical activity for 24 hours. This procedure enables doctors to detect whether the person has abnormal heart rhythms (arrhythmias) or episodes of inadequate blood supply without symptoms (silent ischemia). An exercise stress test (electrocardiography done during exercise) before or shortly after discharge can help determine how well the person is doing after the heart attack and whether ischemia is continuing. If these procedures detect abnormal heart rhythms or ischemia, drug therapy may be recommended. If ischemia persists, doctors may recommend coronary angiography to evaluate the possibility of doing percutaneous coronary intervention or coronary artery bypass grafting to restore blood flow to the heart.

Prognosis of Acute Coronary Syndromes

Many people who have unstable angina go on to have a heart attack within about 3 months.

The most dangerous time for someone who is having a heart attack is during the first few hours and before they go to a hospital. During this period, up to 20 to 30 percent of people with a heart attack may die, so it is critical to seek medical attention immediately when people suspect they are having a heart attack. Most people who survive for a few days after a heart attack can expect a full recovery, but about 10% die within a year. Most deaths occur in the first 3 or 4 months, typically in people who continue to have angina, abnormal heart rhythms originating in the ventricles (ventricular arrhythmias), or heart failure. The prognosis is worse if the heart has enlarged after a heart attack than if heart size remains normal.

Older people are more likely to die after a heart attack and to have complications, such as heart failure. The prognosis for smaller people is worse than that for larger people. This finding may help explain why the prognosis for women who have had a heart attack is, on average, worse than that for men. Women also tend to be older and to have more serious disorders when they have a heart attack. Also, they tend to wait longer after a heart attack to go to the hospital than do men.

Did You Know...

  • Half of deaths due to a heart attack occur in the first 3 or 4 hours after symptoms begin.

Prevention of Acute Coronary Syndromes

For people who have had a heart attack, doctors recommend taking one baby aspirin, one half of an adult aspirin, or one full adult aspirin daily. Because aspirin prevents platelets from forming clots, it reduces the risk of death and the risk of a second heart attack by 15 to 30%. People with an allergy to aspirin may take clopidogrel instead.

For people who have not had a heart attack but who are over 50 years of age and have 2 or more risk factors doctors have also typically recommended taking low-dose aspirin every day to prevent heart attacks and stroke. However, aspirin can sometimes cause complications such as gastrointestinal bleeding, and recent evidence suggests that these complications may counterbalance the possible benefit of aspirin in people who have not had a heart attack. Doctors help people weigh their individual risk and benefit.

Usually, doctors also prescribe a beta-blocker (such as metoprolol) because these drugs reduce the risk of death by about 25%. The more serious the heart attack, the more benefit beta-blockers provide. However, some people cannot tolerate the side effects (such as wheezing, tiredness, erectile dysfunction, and cold limbs), and not everyone benefits.

Taking lipid-lowering drugs will reduce the risk of death after a heart attack. People at high risk (especially obese people with diabetes) who have not yet had a heart attack or stroke may benefit from lipid-lowering drugs.

Angiotensin-converting enzyme (ACE) inhibitors, such as captopril, enalapril, perindopril, trandolapril, lisinopril, and ramipril, are often prescribed after a heart attack. These drugs help prevent death and the development of heart failure, particularly in people who have had a massive heart attack or who develop heart failure.

People should also make changes in their lifestyle. They should eat a low-fat diet and increase the amount of exercise they get. People who have high blood pressure or diabetes should try to keep those disorders under control. People who smoke should quit.

Treatment of Acute Coronary Syndromes

  • Drugs
  • Reopening or bypassing blocked arteries
  • Lifestyle changes

Acute coronary syndromes are medical emergencies. Half of deaths due to a heart attack occur in the first 3 or 4 hours after symptoms begin. The sooner treatment begins, the better the chances of survival. Anyone having symptoms that might indicate an acute coronary syndrome should obtain prompt medical attention. Prompt transportation to a hospital’s emergency department by an ambulance with trained personnel may save the person’s life. Trying to contact the person’s doctor, relatives, friends, or neighbors is a dangerous waste of time.

Did You Know...

  • In a person who is having symptoms that might indicate a heart attack, prompt transportation to a hospital’s emergency department by an ambulance with trained personnel may save the person’s life. Trying to contact the person’s doctor, relatives, friends, or neighbors is a dangerous waste of time.

People who may be having a heart attack are usually admitted to a hospital that has a cardiac care unit. Heart rhythm, blood pressure, and the amount of oxygen in the blood are closely monitored so that heart damage can be assessed. Nurses in these units are specially trained to care for people with heart problems and to handle heart emergencies.

Often, oxygen is given through nasal prongs or a face mask. Providing more oxygen to the heart helps keep heart tissue damage to a minimum.

If no complications occur during the first few days, most people can safely leave the hospital within a few more days. If complications such as abnormal heart rhythms develop or the heart can no longer pump adequately (heart failure), hospitalization can be prolonged.

Drug treatment

The most important issue in the early part of treatment of a heart attack is to get to medical attention quickly so doctors can attempt to restore blood flow in the affected artery. People who think they may be having a heart attack should chew an aspirin tablet immediately after calling an ambulance. If aspirin is not taken at home or given by emergency personnel, it is immediately given at the hospital. This therapy improves the chances of survival by reducing the size of the clot (if present) in the coronary artery. People with an allergy to aspirin may be given clopidogrel, ticlopidine, or ticagrelor instead. Some people are given both aspirin and clopidogrel/ticlopidine/ticagrelor.

People are given drugs to prevent the formation of blood clots, to reduce anxiety, and to reduce the size of the heart. People may need to take these drugs for some time after they have recovered from a heart attack. Drugs are used to reduce the heart's workload during and after a heart attack.

Because decreasing the heart’s workload also helps limit tissue damage, a beta-blocker is usually given to slow the heart rate. Slowing the rate enables the heart to work less hard and reduces the area of damaged tissue.

Most people are also given an anticoagulant drug, such as heparin, to help prevent the formation of additional blood clots.

Most people are given nitroglycerin, which relieves pain by reducing the workload of the heart and possibly by dilating arteries. Usually, it is first given under the tongue, then intravenously. Occasionally, when nitroglycerine cannot be used or is ineffective, doctors give morphine to reduce discomfort and anxiety.

Angiotensin-converting enzyme (ACE) inhibitors can reduce heart enlargement and increase the chance of survival for many people. Therefore, these drugs are usually given in the first few days after a heart attack and prescribed indefinitely.

Statins have long been used to help prevent coronary artery disease, but doctors have recently found that they also have short-term benefit for people with an acute coronary syndrome. Doctors give a statin to people who are not already taking one.

More information on the drugs used to treat heart attack can be found elsewhere in THE MANUAL.

Opening the arteries

The decision on the timing and method of opening a blocked coronary artery depends on the type of acute coronary syndrome and on how quickly the person got to the hospital. There are several ways to open blocked coronary arteries:

  • Percutaneous cardiac interventions
  • Clot-dissolving drugs
  • Bypass surgery (coronary artery bypass grafting)

In people who have an ST-segment elevation MI, immediately clearing the coronary artery blockage saves heart tissue and improves survival. Doctors try to clear the blockage within 90 minutes after the person arrives at the hospital. Because the sooner the artery is cleared the better the outcome, the method of clearing is probably not as important as the timing.

Percutaneous cardiac interventions (PCI), such as angioplasty and stent placement, appear to be the best way to open blocked arteries during an ST-segment elevation MI if they can be done within 90 minutes of the time the person arrives at the hospital.

Clot-dissolving drugs (also called thrombolytic or fibrinolytic drugs—see table Drugs Used to Treat Coronary Artery Disease) are given by vein (intravenously) to open the arteries if PCI procedures are not available within the 90-minute time frame. Thrombolytic drugs include streptokinase, tenecteplase (TNK-tPA), alteplase, and reteplase. Although better if given immediately, these drugs can work well within 3 hours and may be of some benefit for up to 12 hours after the person arrives at the hospital. In some areas, thrombolytic drugs are given before hospital arrival by specially trained paramedics. Most people who are given a thrombolytic drug still need to have PCI before they leave the hospital.

Because thrombolytic drugs can cause bleeding, they are not usually given to people who have bleeding in the digestive tract, who have severe high blood pressure, who have recently had a stroke, or who have had surgery during the month before the heart attack. Older people who do not have any of these conditions can be safely given a thrombolytic drug.

People who have a non-ST-segment elevation MI or unstable angina do not usually benefit from immediate PCI or thrombolytic drugs. However, doctors usually do PCI within the first day or two of hospitalization. If the person’s symptoms worsen or certain complications develop, doctors may do PCI earlier.

In some people, coronary artery bypass grafting (CABG) is done during an acute coronary syndrome instead of using PCI or a thrombolytic drug. For example, CABG may be used for people who cannot be given a thrombolytic drug (for example, because they have a bleeding disorder or have had a recent stroke or recent major surgery). CABG may also be used for people who cannot undergo PCI because of the severity of their arterial disease (for example, because there are many areas of blockage or heart function is poor, especially if the person also has diabetes).

General measures

Because physical exertion, emotional distress, and excitement stress the heart and make it work harder, a person who has just had a heart attack should stay in bed in a quiet room for a few days. Visitors are usually limited to family members and close friends. Watching television may be permitted if the programs do not cause stress.

Smoking, a major risk factor for coronary artery disease, is prohibited in hospitals. Moreover, an acute coronary syndrome is a compelling reason to stop smoking.

Stool softeners and gentle laxatives may be used to prevent constipation, so that the person does not have to strain. If the person cannot pass urine or if the doctors and nurses need to keep track of the precise amount of urine produced, a urinary catheter is used.

For severe nervousness (which can stress the heart), a mild antianxiety drug (for example, a benzodiazepine such as lorazepam) may be prescribed. To deal with mild depression and denial of illness, which are common after acute coronary syndromes, people are encouraged to talk about their feelings with doctors, nurses, social workers, and their family members and friends. Some people require an antidepressant.


After about 2 to 4 days in the hospital, people who have had an uncomplicated heart attack and successful PCI are usually discharged. Other people may require a longer stay.

Nitroglycerin, aspirin and sometimes clopidogrel, a beta-blocker, an angiotensin-converting enzyme (ACE) inhibitor, and a lipid-lowering drug (most often, a statin) are usually prescribed.


Cardiac rehabilitation, an important part of recovery, begins in the hospital. Remaining in bed for longer than 2 or 3 days leads to physical deconditioning and sometimes to depression and a sense of helplessness. Barring complications, people who have had a heart attack can usually progress to sitting in a chair, passive exercise, use of a commode chair, and reading on the first day. By the second or third day, people are encouraged to walk to the bathroom and engage in nonstressful activities, and they can do more activities each day. If everything goes well, people are usually back to their normal activities within about 6 weeks. Participation in a regular exercise program consistent with the person’s age and heart health is beneficial.

Drugs Mentioned In This Article

Generic Name Select Brand Names
streptokinase STREPTASE
nitroglycerin NITRO-DUR
trandolapril MAVIK
tenecteplase TNKASE
ticlopidine No US brand name
clopidogrel PLAVIX
ticagrelor BRILINTA
reteplase RETAVASE
enalapril VASOTEC
captopril CAPOTEN
lorazepam ATIVAN
alteplase ACTIVASE
ramipril ALTACE

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