What actually causes a heart attack?

The Hook

A heart attack usually isn’t your heart “wearing out” — it’s a sudden plumbing emergency that unfolds in minutes.

The Science

Your heart muscle is fed by its own vessels, the coronary arteries. Over years, fatty deposits called plaques can build up inside their walls — a process called atherosclerosis. The dangerous moment is when a plaque ruptures: your body treats it like a wound and forms a blood clot, which can abruptly block the artery.

Downstream, the heart muscle is starved of oxygen (ischemia) and, within minutes to hours, begins to die. That dying muscle is the heart attack — medically, a myocardial infarction.

A key and counterintuitive point: the plaques most likely to rupture often aren’t the biggest ones. A large, stable plaque may narrow an artery for years and mostly cause warning symptoms like chest pain on exertion. But a smaller plaque with a thin, inflamed cap can burst without warning, which is part of why heart attacks can strike people who felt fine the day before. It’s the instability of the plaque, not just its size, that makes it dangerous.

This is also why the classic symptoms make sense. Chest pressure, pain spreading to the arm or jaw, sweating, and shortness of breath are all signs of a heart muscle suddenly short on oxygen. Symptoms can be subtler in some people — including women, older adults, and people with diabetes — which is exactly why acting quickly on any suspicion, rather than waiting for certainty, saves muscle and lives.

Three Wild Facts

• The most dangerous plaques are often not the largest; a small, unstable one with a thin cap can rupture while a big, stable one quietly narrows an artery for years.
• Heart muscle has very limited ability to regenerate, so tissue lost in a heart attack is usually replaced by scar rather than new muscle — making prevention and speed all the more important.
• Because “time is muscle,” every minute of a blocked artery costs living heart tissue, which is why emergency teams race to reopen the vessel with clot-busting drugs or a stent.

Why It Matters

It explains why heart attacks feel sudden even though the setup took decades, and why speed of treatment matters so much — “time is muscle.” It’s also why prevention targets the slow buildup (blood pressure, cholesterol, smoking) long before the emergency. The takeaway is simple: the years give you leverage to prevent it, and the minutes decide how much is saved.