An MI, short for myocardial infarction, is the medical term for a heart attack. It happens when blood flow to part of the heart muscle gets blocked long enough for that tissue to start dying. About 805,000 people in the United States have one every year, and roughly 1 in 5 are “silent,” meaning the person doesn’t realize it’s happening at the time.
How a Heart Attack Happens
Your heart muscle needs a constant supply of oxygen-rich blood, delivered through the coronary arteries. Over years, fatty deposits called plaques can build up inside these arteries. A heart attack typically starts when one of those plaques cracks open. The body treats the crack like a wound and forms a blood clot over it, but that clot can completely block the artery.
Once blood flow stops, the heart muscle downstream begins to suffer. If the blockage lasts more than 20 to 40 minutes, cells start to die. The damage begins in the innermost layer of the heart wall and spreads outward over time. The outer layers survive a bit longer because they have more backup blood supply from neighboring vessels, but without treatment the damage keeps expanding. The longer the artery stays blocked, the more muscle is permanently lost.
STEMI vs. NSTEMI
Doctors classify heart attacks into two main types based on what an electrocardiogram (ECG) shows. A STEMI (ST-elevation myocardial infarction) produces a specific electrical pattern indicating a complete blockage of a coronary artery. It’s treated as the most urgent scenario, requiring emergency procedures to reopen the artery as fast as possible.
An NSTEMI (non-ST-elevation myocardial infarction) doesn’t show that same pattern on the ECG. It’s traditionally associated with a partial blockage and damage limited to the inner lining of the heart. However, this distinction isn’t perfect. Studies show that about 1 in 4 NSTEMI patients actually do have a completely blocked artery, and those people tend to have worse outcomes than other NSTEMI patients. Both types are serious medical emergencies.
Symptoms in Men and Women
The classic heart attack symptom is intense chest pressure or pain, sometimes described as a heavy weight sitting on the chest. This can radiate into the left arm, neck, or jaw. Many people also experience shortness of breath, cold sweats, and nausea.
Women, however, frequently experience a different set of symptoms. Chest pain may not be the most prominent sign, or it may be absent entirely. Instead, women more commonly report unusual fatigue, dizziness, nausea or vomiting, back or jaw pain, shortness of breath, and discomfort in the upper abdomen. These symptoms can come on during rest or even during sleep, which makes them easier to dismiss as something less serious. This difference in presentation is one reason heart attacks in women are more likely to be diagnosed late.
Major Risk Factors
Five modifiable risk factors account for nearly 60% of all cardiovascular disease cases: high blood pressure, diabetes, high cholesterol, smoking, and obesity. These are the factors you can do something about, and they carry the most statistical weight.
Non-modifiable risk factors include age, sex (men develop heart disease earlier on average, though women catch up after menopause), family history, and genetics. Beyond these standard categories, less obvious contributors include chronic inflammation, sleep disorders, air pollution, mental health conditions, and even poor oral health. Some people have heart attacks without any of the classic risk factors, which underscores the role these less-recognized risks can play.
How It’s Diagnosed
When you arrive at an emergency room with suspected heart attack symptoms, two tests happen quickly: an ECG and a blood test for troponin. Troponin is a protein that leaks from damaged heart cells into the bloodstream. Current guidelines use a baseline threshold of 52 nanograms per liter on high-sensitivity troponin tests as the initial decision point. If your level is above that, it signals possible heart damage. Doctors will typically retest after a few hours to see if the number is rising, which helps distinguish an active heart attack from other causes of elevated troponin.
The ECG records the heart’s electrical activity and can reveal the specific patterns that separate a STEMI from an NSTEMI. In some cases, a coronary angiogram (where dye is injected into the arteries and viewed on X-ray) is used to pinpoint exactly where the blockage is located.
Emergency Treatment
If you think someone is having a heart attack, calling emergency services is the most important step. While waiting, have the person chew a full-dose aspirin (325 mg) unless they’re allergic. Chewing gets it into the bloodstream faster than swallowing it whole. If the person has been prescribed nitroglycerin for a known heart condition, help them take it. If chest pain doesn’t improve within three minutes of taking nitroglycerin, that’s another signal to get emergency help immediately.
At the hospital, the priority for a STEMI is reopening the blocked artery. This is usually done through a procedure called percutaneous coronary intervention (PCI), where a thin catheter is threaded into the coronary artery and a small balloon is inflated to widen the blockage, often followed by placing a stent to keep the artery open. For patients with severe blockages in multiple arteries, left main artery disease, or diabetes with complex coronary disease, bypass surgery (CABG) may be the better option. Both approaches effectively relieve symptoms, but patients who receive stents are more likely to need repeat procedures down the line.
Complications to Watch For
The danger doesn’t end once the blockage is treated. Complications can develop on different timelines depending on how much muscle was damaged.
- First 24 hours: Cardiogenic shock (where the heart can’t pump enough blood to meet the body’s needs) and heart failure. These are most common with large heart attacks affecting the front wall of the heart.
- Days 1 to 3: Abnormal heart rhythms, including dangerous ones that originate in the lower chambers. Heart block, where electrical signals between the upper and lower chambers are disrupted, can also develop.
- First week to first month: Mechanical complications, including tears in the heart’s internal structures, weakening of the heart wall, or fluid accumulating around the heart.
- Weeks to months: Inflammation of the sac surrounding the heart (pericarditis) can develop, sometimes as a delayed immune response known as Dressler syndrome.
Recovery and Cardiac Rehab
Recovery from a heart attack follows a structured path. Cardiac rehabilitation happens in three phases, and it’s one of the most effective tools for preventing a second event.
Phase 1 begins while you’re still in the hospital. It focuses on gentle movement, education about what happened to your heart, and planning for discharge. Phase 2 is an outpatient program where you attend supervised exercise sessions, typically two or three times per week. You’ll start at a low intensity and gradually increase as your fitness and confidence improve. Your rehab team sets personalized training zones based on your medical history and current heart function. Phase 3 is the long-term maintenance stage, where you continue exercising on your own using the habits and knowledge built during the supervised phases.
Beyond exercise, rehab programs address diet, stress management, medication adherence, and the emotional side of recovery. Depression and anxiety after a heart attack are common, and addressing them is a standard part of the process.