A heart attack happens when blood flow to part of the heart muscle is suddenly blocked, usually by a blood clot forming on top of a fatty deposit inside a coronary artery. Without blood flow, heart muscle cells start dying within minutes. The underlying process that sets the stage for this event typically builds over years or even decades, but the final trigger can strike in seconds.
How Plaque Builds in Your Arteries
The process begins with damage to the inner lining of a coronary artery. High blood pressure, smoking, high cholesterol, and chronic inflammation all contribute to this damage. Once the lining is compromised, LDL cholesterol particles slip beneath the artery wall and become trapped. White blood cells follow, absorbing the cholesterol and swelling into what scientists call “foam cells.” These foam cells cluster together to form a fatty streak, the earliest visible sign of heart disease.
Over time, smooth muscle cells migrate into the area, and collagen accumulates alongside more foam cells. The result is a plaque: a lump of fatty material, inflammatory cells, and scar tissue sitting inside the artery wall. A fibrous cap forms over the top, separating the plaque’s contents from the bloodstream. As plaque grows, the artery narrows. When the blockage reaches about 70%, blood flow becomes restricted enough to cause chest pain during exercise or stress. At 90% blockage, symptoms can appear even at rest.
What Triggers the Actual Heart Attack
Most heart attacks don’t happen because a plaque slowly closes off an artery. They happen because a plaque ruptures. The fibrous cap covering the plaque cracks open, exposing the fatty, inflammatory material inside directly to the bloodstream. The body treats this like an injury and launches its clotting response. Platelets rush to the site and stick to the exposed tissue, releasing chemical signals that recruit even more platelets. Within minutes, a blood clot can form large enough to completely block the artery.
The plaques most likely to rupture aren’t necessarily the biggest ones. They tend to be softer, with a thin fibrous cap and a large core of inflammatory material. Enzymes released by immune cells inside the plaque actively weaken the cap, making it more fragile. This is why someone can have a heart attack with no prior warning: a plaque that wasn’t restricting blood flow enough to cause symptoms can still rupture catastrophically.
Risk Factors That Accelerate the Process
High LDL cholesterol is the primary fuel for plaque growth. Every 39 mg/dL reduction in LDL cholesterol is associated with roughly a 22% drop in cardiovascular events. For people already at high risk, treatment guidelines aim for LDL levels below 70 mg/dL, while moderate-risk individuals typically target below 100 mg/dL. Genetic data reinforces how important this is: people born with gene variants that keep their LDL about 10 mg/dL lower throughout life have a 16 to 18% lower risk of heart disease.
High blood pressure accelerates arterial damage at every level. Data from studies involving over a million people shows that heart disease death rates rise in a straight line starting from blood pressures as low as 115/75. For every 20-point rise in systolic pressure (the top number), mortality from heart disease doubles. Even blood pressure in the 130-139/85-89 range carries more than twice the cardiovascular risk compared to readings below 120/80.
A genetic factor called lipoprotein(a) deserves special mention because it’s entirely inherited and largely unaffected by diet or exercise. About 10 to 30% of the global population (roughly 1.4 billion people) have elevated levels. High lipoprotein(a) doubles the risk of coronary artery disease. It works by carrying a heavy load of oxidized fats that promote inflammation and plaque instability, making it more dangerous than regular LDL cholesterol on a particle-for-particle basis. Most standard cholesterol panels don’t measure it, so many people with elevated levels don’t know.
Diabetes, smoking, obesity, and a sedentary lifestyle round out the major risk factors. Each one contributes to the inflammation, arterial stiffness, and metabolic dysfunction that feed plaque growth.
Acute Triggers That Set Off an Event
On top of long-term risk factors, specific short-term triggers can push a vulnerable plaque to rupture or provoke a clot. These triggers raise heart rate, spike blood pressure, or cause a surge of stress hormones that increase shear force on artery walls.
- Heavy physical exertion: The risk of a heart attack is about 6 times higher during or immediately after intense exercise compared to rest. This is especially dangerous for people who are sedentary most of the time but occasionally push hard.
- Intense anger: Episodes of anger raise heart attack risk 2 to 9 times in the hours that follow, depending on the study and intensity of the emotion.
- Work stress: Having a high-pressure deadline at work is linked to a six-fold increase in heart attack risk within the following 24 hours.
- Sexual activity: Carries about a 2.5-fold increased risk in the two hours afterward, though the absolute risk remains low for most people.
- Heavy meals: Eating a large meal can raise heart attack risk roughly 4 times in the hours that follow, likely due to spikes in blood flow to the digestive system and changes in blood clotting.
- Cocaine use: The most dangerous acute trigger studied, with a nearly 24-fold increase in heart attack risk in the hour after use.
- Cold weather: Each 1°C drop in daily mean temperature is associated with a measurable increase in heart attack risk over the following weeks.
- Air pollution: Short-term spikes in fine particulate matter (PM2.5) contribute to tens of thousands of early cardiovascular deaths per year in the United States alone.
Heart Attacks Without Major Blockages
Not every heart attack follows the classic plaque-rupture script. Some people, especially women, have heart attacks with clean or only mildly narrowed arteries. This is called MINOCA (myocardial infarction with non-obstructive coronary arteries), and it has several possible causes.
Coronary vasospasm is one: the artery suddenly clamps down, cutting off blood flow temporarily. Microvascular dysfunction involves the tiny blood vessels within the heart muscle itself failing to deliver adequate blood, even though the large arteries look fine. Spontaneous coronary artery dissection (SCAD) occurs when the wall of a coronary artery tears, and blood collects between the layers, compressing the artery from the inside. About 90% of SCAD patients are women, typically in their 40s and 50s, often without any traditional cardiovascular risk factors. Extreme physical or emotional stress precedes the event in roughly 40% and 24% of cases, respectively. SCAD is the leading cause of heart attacks in young women, including those who are pregnant or recently gave birth.
How Symptoms Differ by Sex
The classic heart attack presentation involves crushing chest pain radiating to the left arm, along with sweating and shortness of breath. This pattern is more common in men. Women are significantly more likely to experience what doctors call atypical symptoms: dizziness, nausea or vomiting, back pain (particularly between the shoulder blades), extreme fatigue, palpitations, or fainting. In one study, 85% of women presented with atypical symptoms compared to 70% of men.
When women did have chest pain, they more often described it as tightness or squeezing and were more likely to feel it in the upper chest or between the shoulder blades rather than behind the breastbone. Women also tended to have their heart attacks between 6 a.m. and noon, while men more often had them between midnight and 6 a.m. These differences matter because atypical symptoms lead to delays in seeking care, which means more heart muscle damage by the time treatment begins.