The Human Circulatory System

What Is a Heart Attack?

Heart Attack

A heart attack, also known as a myocardial infarction, happens when the flow of blood that brings oxygen to a part of your heart muscle suddenly becomes blocked. Your heart can’t get enough oxygen. If blood flow is not restored quickly, the heart muscle will begin to die.

Heart attacks are very common. According to the Centers for Disease Control and Prevention, more than 800,000 people in the United States have a heart attack each year.

A heart attack is not the same as cardiac arrest, which happens when your heart suddenly and unexpectedly stops beating. A heart attack can cause sudden cardiac arrest.

Most heart attacks are caused by coronary artery disease. Your age, lifestyle habits, and other medical conditions can raise your risk of a heart attack. Symptoms of a heart attack include chest and upper body pain, shortness of breath, dizziness, sweatiness, and nausea. Women often experience different symptoms of a heart attack.

If you think you or someone else may be having a heart attack, call 9-1-1 right away. Acting fast can save your life. The longer the heart goes without enough oxygen, the more damage is done to the heart muscle.

What causes a heart attack?

The most common cause of a heart attack is coronary artery disease, which is the most common type of heart disease. This is when your coronary arteries cannot carry enough oxygen-rich blood to your heart muscle. Most of the time, coronary artery disease happens when a waxy substance called plaque builds up inside your arteries, causing the arteries to narrow. The buildup of this plaque is called atherosclerosis. This can happen over many years, and it can block blood flow to parts of your heart muscle. Plaques that narrow arteries slowly over time cause angina.

Eventually, an area of plaque can break open inside your artery. This causes a blood clots to form on the plaque’s surface. If the clot becomes large enough, it can block blood flow to your heart. If the blockage isn’t treated quickly, a part of your heart muscle begins to die.

Other causes of a heart attack

Not all heart attacks are caused by blockages from atherosclerosis. When other heart and blood vessel conditions cause a heart attack, it is called myocardial infarction in the absence of obstructive coronary artery disease (MINOCA). MINOCA is more common in women, younger people, and racial and ethnic minorities, including Black, Hispanic/Latino, and Asian people.

Conditions that can cause MINOCA have different effects on the heart.

  • Small plaques in your arteries may not block your blood vessels, but they can break open or their outer layer can wear away. This can cause blood clots to form on these plaques. The blood clots can then block blood flow through your coronary arteries. The formation of small plaques is more common in women, people who smoke, and people who have other blood vessel conditions.
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  • A sudden and serious spasm (tightening) of your coronary artery can block blood flow through your artery, even if there isn’t a buildup of plaque. Smoking is a risk factor for a coronary spasm. If you smoke, you may be more likely to have a spasm triggered by extreme cold or very stressful situations. Drugs like cocaine may also cause coronary spasm.
  • A coronary artery embolism occurs when a blood clot travels through your bloodstream and gets stuck in your coronary artery. This can block blood flow through your artery. This is more common in people who have atrial fibrillation or conditions that raise the risk of blood clots, such as thrombocytopenia or pregnancy.
  • Spontaneous coronary artery dissection (SCAD) occurs when a tear forms inside your coronary artery. A blood clot can then form at the tear, or the torn tissue itself can block your artery. SCAD can be caused by stress, extreme physical activity, and pregnancy. This condition is more common in women who are under 50 years old or pregnant and in people who have Marfan syndrome.

What are the symptoms of a heart attack?

If you are having a heart attack, you may experience one or more of the symptoms below.

  • Chest pain, heaviness, or discomfort in the center or left side of the chest (this is the most common symptom)
  • Pain or discomfort in one or both arms, your back, shoulders, neck, jaw, or above your belly button
  • Shortness of breath when resting or doing a little bit of physical activity (this is more common in older adults)
  • Sweating a lot for no reason
  • Feeling unusually tired for no reason, sometimes for days (this is more common in women)
  • Nausea (feeling sick to the stomach) and vomiting
  • Light-headedness or sudden dizziness
  • Rapid or irregular heartbeat

It is also possible to have mild symptoms or even no symptoms at all and still have a heart attack.

When to call 9-1-1

Any time you think you might be having a heart attack, don’t ignore it. Call 9-1-1 for emergency medical care, even if you are not sure that you’re having a heart attack.

  • Acting fast can limit damage to your heart and save your life. The 9-1-1 operator or emergency medical services (EMS) personnel can give you advice that can help prevent damage to your heart.
  • An ambulance is the best and safest way to get to the hospital. Do not drive to the hospital or let someone else drive you. EMS personnel can check how you are doing and start tests and lifesaving medicines right away. People who arrive by ambulance often get faster treatment at the hospital.

Every minute matters. Never delay calling 9-1-1, taking aspirin or doing anything else you think might help.

Knowing the difference between stable angina (chest pain in people who have coronary artery disease) and a heart attack is important.

  • The pain from angina usually happens after physical activity and goes away in a few minutes when you rest or take medicine to treat it.
  • The pain from a heart attack is more serious than the pain from angina. Heart attack pain doesn’t go away when you rest or take medicine.

If you don’t know whether your chest pain is angina or a heart attack, call 9-1-1.

Diagnosis of Heart Attack

Calling 9-1-1 for an ambulance and getting to the emergency room quickly if you suspect a heart attack is critical. Once at the hospital, you will likely get tests to see whether you are having a heart attack or whether you have already had one.

An electrocardiogram (EKG) is the most common initial test and may be given within minutes of your arrival at the hospital. An EKG will check whether you may be having a heart attack.

Based on the results of the EKG, your doctor may then order more tests, ask you about your medical history, and do a physical exam.

Blood tests: During a heart attack, heart muscle cells die and release proteins into your bloodstream. Blood tests can measure the amount of these proteins in your blood. For example, you may get a troponin test to measure the amount of a protein called troponin in your blood. Troponin leaks when heart muscle cells die during a heart attack.

Blood tests often are repeated to check for changes over time.

Heart imaging tests: Imaging tests, such as a chest X-ray or computed tomography (CT) help your doctor check whether your heart is working properly. You may also need a stress test, which can help your doctor determine the amount of damage to your heart or if the cause of the heart attack is coronary artery disease.

Treatment of Heart Attack


  • Aspirin or other medicines can prevent more blood clots from forming. In some people, aspirin may cause bleeding in the stomach.
  • Nitroglycerin, or nitrates, can make it easier for your heart to pump blood and to improve blood flow through your coronary arteries. Nitroglycerin also treats chest pain. You may also be given other medicines for chest pain. Side effects of this medicine include nausea, vomiting, weakness, a slow heartbeat, and low blood pressure.
  • Thrombolytic medicines, also called clot busters, can help dissolve blood clots that are blocking your coronary arteries. These medicines may cause bleeding problems. You may be given these if you were unable to reach a hospital that can do a percutaneous coronary intervention (see below) quickly enough.

Oxygen therapy: Oxygen therapy is a treatment that delivers oxygen gas for you to breathe. You can receive oxygen therapy from tubes resting in your nose, a face mask, or a tube placed in your trachea (windpipe). You may need oxygen therapy if you have a condition that causes your blood oxygen levels to be too low.

Oxygen therapy can be given for a short or long period of time in the hospital, another medical setting, or at home. Oxygen poses a fire risk, so you should never smoke or use flammable materials when using oxygen. You may experience side effects from this treatment, such as a dry or bloody nose, tiredness, and morning headaches. Oxygen therapy is generally safe.

Procedures: You may need one of the following procedures at the hospital or later to help restore blood flow to your heart. These procedures are often done as soon as your healthcare team confirms that you are having a heart attack.

Percutaneous coronary intervention: Percutaneous coronary intervention (PCI), also called coronary angioplasty, is a nonsurgical procedure that improves blood flow to your heart. Doctors use PCI to open blood vessels to the heart that are narrowed or blocked by buildup of plaque. PCI requires cardiac catheterization.

A cardiologist, the doctor who specializes in the heart, performs PCI in a hospital cardiac catheterization laboratory. Live X-rays help your doctor guide a catheter through your blood vessels into your heart, where special contrast dye is injected to highlight any blockage. To open a blocked artery, your doctor will insert another catheter over a guidewire and inflate a balloon at the tip of that catheter. Your doctor may also put a small mesh tube called a stent in your artery to help keep the artery open.

You may develop a bruise and soreness where the catheters were inserted. It also is common to have discomfort or bleeding where the catheters were inserted. You will recover in a special unit of the hospital for a few hours or overnight. You will get instructions on how much activity you can do and what medicines to take. You will need a ride home because of the medicines and anesthesia you received. Your doctor will check your progress during a follow-up visit. If a stent is implanted, you will have to take certain anticlotting medicines exactly as prescribed, usually for at least 6 to 12 months.

Serious complications during a PCI procedure or as you are recovering after one are rare, but they can happen. This might include:

  • Bleeding
  • Blood vessel damage
  • Treatable allergic reaction to the contrast dye
  • Need for emergency coronary artery bypass grafting during the procedure
  • Arrhythmias, or irregular heartbeats
  • Damaged arteries
  • Kidney damage
  • Heart attack
  • Stroke
  • Blood clots

Sometimes chest pain can occur during PCI because the balloon briefly blocks blood supply to the heart. Restenosis, when tissue regrows where the artery was treated, may occur in the months after PCI. This may cause the artery to become narrow or blocked again. The risk of complications from this procedure is higher if you are older, have chronic kidney disease, are experiencing heart failure at the time of the procedure, or have extensive heart disease and more than one blockage in your coronary arteries.


Stenting: A stent is a small mesh tube that holds open passages in the body, such as weak or narrow arteries. Stenting is a minimally invasive procedure. The most common complication after a stenting procedure is a blockage or blood clot in the stent. You may need to take certain medicines, such as aspirin and other anti-platelet medicines, for a year or longer after receiving a stent in your artery to prevent serious complications such as blood clots.

Coronary artery bypass grafting (CABG): CABG is a procedure to improve poor blood flow to the heart. It may be needed when the arteries supplying blood to heart tissue, called coronary arteries, are narrowed or blocked. This surgery may lower the risk of serious complications for people who have a type of heart disease called obstructive coronary artery disease. CABG may also be used in an emergency, such as a severe heart attack.



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