A heart attack happens when blood flow to part of the heart muscle is suddenly cut off, usually by a blood clot that forms inside a coronary artery. Without blood delivering oxygen, heart cells begin to die in as little as 10 minutes. In the United States, someone has a heart attack roughly every 40 seconds, adding up to about 605,000 first-time attacks and 200,000 recurrent attacks each year.
It Starts With Plaque Buildup
The process behind most heart attacks begins years or even decades before any symptoms appear. It starts when cholesterol particles (specifically LDL, the “bad” cholesterol) slip into the inner wall of a coronary artery and become trapped. Once stuck there, these particles undergo chemical changes, becoming oxidized. The immune system treats them as foreign invaders, sending white blood cells to the site. Those white blood cells swallow the oxidized cholesterol, swell up, and eventually die, leaving behind a growing core of fatty debris inside the artery wall.
Over time, this process of inflammation, cell death, and scarring builds a structure called a plaque. A fibrous cap, like a thin shell, forms over the fatty core and separates it from the flowing blood. As long as that cap holds, the plaque may narrow the artery and limit blood flow, but it won’t trigger a sudden heart attack. The real danger comes when the cap weakens.
Why Plaques Rupture
Not all plaques are equally dangerous. The ones most likely to cause a heart attack tend to have a large, soft core of dead cells and cholesterol covered by an extremely thin fibrous cap. Chronic inflammation inside the plaque is what thins that cap. Immune cells release enzymes that digest the cap’s structural proteins, weakening it the way rust weakens a metal beam.
Systemic inflammation plays a role too. C-reactive protein (CRP), a marker your doctor may test for, doesn’t just signal inflammation. It actually accumulates inside plaques and increases oxidative stress in the artery wall, further destabilizing the cap. People with higher blood levels of CRP tend to have more of it concentrated in their artery plaques, creating a feedback loop between body-wide inflammation and local plaque instability.
When the cap finally breaks open, the fatty, cell-rich core is exposed to the bloodstream. This material is intensely reactive. Platelets rush to the site and begin clumping together, and the blood’s clotting system activates. Within minutes, a clot can grow large enough to completely block the artery.
Where Blockages Tend to Form
Your heart is fed by three major coronary arteries: the left anterior descending (LAD), the right coronary artery (RCA), and the left circumflex (LCx). Heart attack-causing blockages don’t occur randomly along these vessels. They cluster heavily in the first few centimeters near each artery’s origin. In the LAD, 50% of blockages occur within the first 25 millimeters, and 90% within the first 40 millimeters. The pattern is similar in the other arteries.
This matters because blockages near the origin of a large artery cut off blood to a much larger territory of heart muscle than blockages farther downstream. It’s one of the main reasons heart attacks can be so damaging. A clot just a couple of centimeters down a major artery can starve a substantial portion of the heart.
What Happens to Heart Muscle Without Blood
Once a coronary artery is blocked, the clock starts immediately. Within about 10 minutes, cells in the affected area show visible signs of stress: their energy stores deplete, internal structures begin to break down, and the membranes holding them together start to fail. If blood flow isn’t restored within the next few hours, those cells die through a combination of necrosis (direct cell death from lack of oxygen) and apoptosis (a programmed self-destruction process).
The damage spreads outward from the core of the oxygen-starved zone. Cells closest to the blockage die first. Cells at the edges, which may get some residual blood flow from neighboring vessels, can survive longer. This is why fast treatment makes such a dramatic difference. Reopening the artery even 60 to 90 minutes sooner can save a meaningful amount of heart muscle.
How the Heart Heals
The heart cannot regenerate lost muscle. Instead, the body replaces dead heart cells with scar tissue, a process that unfolds over weeks. New blood vessels grow into the damaged area to support the repair cells, which are primarily fibroblasts that produce collagen. This scar tissue is structurally different from heart muscle. It’s stiffer, it doesn’t contract, and it doesn’t conduct electrical signals.
The scar itself is not a static patch. It remains metabolically active, continuing to remodel and turn over collagen long after the initial injury. Over time, the scar thins and contracts, which can change the shape of the heart chamber and affect how well the heart fills and pumps. The extent of this remodeling depends largely on how much muscle was lost. A small heart attack may leave the heart functioning nearly normally, while a large one can lead to lasting heart failure.
Heart Attacks Without Major Blockages
About 5 to 6% of heart attacks occur in people whose coronary arteries show no significant blockage on imaging. This condition, called MINOCA (myocardial infarction with nonobstructive coronary arteries), has several possible causes. A coronary artery can go into sudden spasm, clamping down hard enough to stop blood flow temporarily. The tiny blood vessels deep within the heart muscle can malfunction, cutting off circulation at a microscopic level. Other causes include a spontaneous tear in an artery wall (coronary dissection), a blood clot that traveled from elsewhere in the body, or inflammation of the heart muscle itself.
How Heart Attacks Differ in Women
Women tend to have their first heart attack about six years later than men, at an average age of 72 compared to 65.6. But the differences go deeper than timing. Women’s coronary arteries are physically smaller and carry higher blood flow relative to their size, which creates different patterns of stress on the artery walls. These differences in blood flow dynamics affect how and where disease develops.
In men, heart attacks most often result from a single large plaque rupturing in a major artery. Women are more likely to have disease spread diffusely across the artery walls or concentrated in the smallest blood vessels of the heart, a pattern called microvascular dysfunction. In one study of patients with chest pain but no major blockages, 77% were women. Nearly all had some degree of atherosclerosis when examined closely, and 44% showed significant problems with how their artery walls responded to signals that should have triggered them to relax and widen.
This means standard tests that look for a single large blockage can sometimes miss heart disease in women. It also means that a heart attack in a woman may involve a different mix of mechanisms: not just a ruptured plaque and a clot, but also artery spasm, widespread narrowing, and dysfunction in vessels too small to see on a standard angiogram.
How Doctors Confirm a Heart Attack
When heart cells die, they release a protein called troponin into the bloodstream. A blood test can detect troponin at very low levels. Normal troponin I is below 0.04 nanograms per milliliter, and normal troponin T is below 0.01. A result above the 99th percentile of what’s expected in healthy adults signals heart muscle damage. Troponin levels typically rise within a few hours of a heart attack and can remain elevated for days, giving doctors a reliable window for diagnosis.
An electrocardiogram (ECG) helps determine what type of heart attack is occurring. When the blockage completely cuts off blood flow to a large area, the ECG often shows a characteristic pattern called ST-segment elevation, which identifies the emergency as a STEMI. This type requires immediate treatment to physically reopen the artery, either with a catheter or clot-dissolving medication. When the ECG doesn’t show that specific pattern, the event is classified as an NSTEMI, which still involves heart muscle damage but typically means the artery isn’t completely blocked or the affected area is smaller. Both are genuine heart attacks, but the urgency and treatment approach differ.