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, causing that tissue to die from lack of oxygen. About 805,000 people in the United States have a heart attack every year, and roughly 1 in 5 of those are “silent,” meaning the person doesn’t realize it’s happening.
What Happens Inside the Heart During an MI
A heart attack doesn’t start with the heart itself. It starts in the coronary arteries, the blood vessels that supply oxygen to heart muscle. Over years, cholesterol deposits build up inside these artery walls, forming what’s called plaque. For a long time, the plaque can sit there without causing problems. The trouble begins when the thin cap covering the plaque cracks open.
Once that cap ruptures, the fatty, inflammatory material inside the plaque is suddenly exposed to the bloodstream. Your body treats this like an open wound. Platelets rush to the site and start clumping together, forming a blood clot. That clot can partially or completely block the artery. When the blockage cuts off blood flow, the heart muscle downstream starts to die. The longer the artery stays blocked, the more muscle is lost. This is why speed matters so much during a heart attack: every minute without blood flow means more permanent damage.
STEMI vs. NSTEMI: Two Types of Heart Attack
Doctors classify heart attacks into two main types based on what they see on an electrocardiogram (ECG). A STEMI (ST-elevation myocardial infarction) shows a distinctive change in the heart’s electrical pattern on the ECG, signaling that a coronary artery is completely blocked. The damage in a STEMI typically extends through the full thickness of the heart wall.
An NSTEMI (non-ST-elevation myocardial infarction) doesn’t show that same ECG pattern. It was traditionally thought to involve only a partial blockage, with damage limited to the inner layer of the heart muscle. But this distinction isn’t always clean. Roughly 25% to 30% of NSTEMI patients actually have a completely blocked artery when doctors look at imaging, and those patients tend to have worse short-term outcomes than NSTEMI patients with partially open arteries.
Both types are confirmed with a blood test that measures troponin, a protein released when heart cells are damaged. Levels above 16 ng/L in women and 34 ng/L in men indicate heart muscle injury.
Recognizing the Symptoms
The classic heart attack feels like chest pain or pressure, often described as squeezing, tightness, burning, or heaviness in the center of the chest. That pain can radiate into the neck, shoulder, or left arm. This is what most people picture when they think of a heart attack, and it’s the most recognized presentation.
But many heart attacks don’t look like that, especially in women. About 85% of women present with what doctors call “atypical” symptoms: dizziness, sweating, shortness of breath, nausea or vomiting, palpitations, fainting, back pain, or unexplained fatigue. Men also experience atypical symptoms, though less frequently (around 70%). Older adults are particularly likely to have a heart attack without obvious chest pain, which partly explains why so many heart attacks go unrecognized.
How a Heart Attack Is Treated
For a STEMI, the priority is opening the blocked artery as fast as possible. The standard procedure involves threading a thin catheter through a blood vessel to the blockage site and inflating a tiny balloon to reopen the artery, usually placing a small metal stent to keep it open. The American College of Cardiology and the American Heart Association recommend that this procedure happen within 90 minutes of the patient arriving at the hospital. That 90-minute window, called “door-to-balloon time,” is the benchmark hospitals are measured against.
NSTEMI treatment follows a similar path but with less urgency. Doctors stabilize the patient with medications first, then often perform the same catheter-based procedure within hours or days depending on the patient’s risk level.
Complications After a Heart Attack
The most common complication is heart failure, where the damaged heart can no longer pump blood efficiently. This has become less frequent with modern treatments. In the mid-1990s, about 46% of heart attack patients developed heart failure during their hospital stay. By 2008, with improvements in how quickly blocked arteries are reopened, that number dropped to 28%.
Even after leaving the hospital, the risk doesn’t disappear. About 13% of heart attack survivors develop heart failure within 30 days, and 20% to 30% develop it within the first year. After that initial period, the risk stabilizes at roughly 1.3% to 2.2% per year. The amount of heart muscle lost during the attack is the biggest factor in whether heart failure develops.
Irregular heart rhythms are another concern. New-onset atrial fibrillation, a type of irregular heartbeat, complicates anywhere from 2% to 21% of heart attack cases. More dangerous rhythm problems, like the heart’s lower chambers quivering instead of pumping, can happen in the first hours after an MI and are a leading cause of sudden death.
Recovery and Cardiac Rehabilitation
Recovery from a heart attack follows a structured path. Phase I begins while you’re still in the hospital. Physical therapists start with the basics: sitting up in bed, performing simple arm and leg movements, then progressing to short walks around the unit. The goal is to restore basic mobility before discharge, and everything is tailored to how much damage your heart sustained.
Phase II starts after you go home. In Europe, these outpatient programs typically run 6 to 12 weeks, though some last up to 24 weeks. In the United States, the timeline depends heavily on insurance coverage, with programs ranging from 6 to 36 supervised sessions over 2 to 18 weeks. Sessions involve monitored exercise that gradually increases in intensity, along with education about diet, medications, stress management, and recognizing warning signs of future problems.
Beyond the formal program, cardiac rehabilitation is also about building habits that reduce the chance of a second heart attack. Most of the long-term risk reduction comes from consistent exercise, blood pressure control, cholesterol management, and quitting smoking if applicable. The first few months after a heart attack carry the highest risk for complications, which is why the structured rehab process starts early and builds gradually.