Heart attacks happen when blood flow to part of the heart muscle gets cut off, starving that tissue of oxygen. The most common cause is a buildup of fatty plaque inside the coronary arteries that suddenly ruptures and triggers a blood clot. But plaque rupture isn’t the only path to a heart attack. Artery spasms, tears in the artery wall, and even sleep disorders can set one in motion.
Plaque Buildup and Rupture
The vast majority of heart attacks trace back to atherosclerosis, a slow process where fat, cholesterol, and other substances accumulate inside the artery walls. This buildup, called plaque, starts small. Over years or decades, it grows layer by layer as cells absorb cholesterol, die, and leave behind debris. A fibrous cap made of smooth muscle cells forms over the plaque, acting like a seal to keep it stable.
The danger isn’t always the size of the plaque. A heart attack typically occurs when that fibrous cap cracks open or erodes. The constant force of blood flowing past the plaque can weaken the cap over time, and when it finally breaks, the body reacts the same way it would to any wound: it forms a clot. That clot can partially or completely block the artery, cutting off blood supply to the heart muscle downstream. If blood flow isn’t restored within roughly an hour, heart tissue begins to die permanently.
What makes this especially dangerous is that plaque can grow for decades without producing symptoms. Many people don’t know they have significant atherosclerosis until a rupture occurs.
The Major Risk Factors Behind Plaque
Several well-established conditions accelerate plaque buildup and make existing plaque more likely to rupture:
- High blood pressure damages artery walls over time, creating rough spots where cholesterol can accumulate more easily. It also increases the physical force pushing against existing plaque.
- High LDL cholesterol provides more raw material for plaque formation. The more LDL circulating in your blood, the more that gets deposited into artery walls.
- Smoking injures the lining of arteries, promotes inflammation, and makes blood more likely to clot. It’s one of the strongest modifiable risk factors.
- Diabetes accelerates atherosclerosis through multiple pathways, including chronic inflammation and damage to blood vessel walls from elevated blood sugar.
- Obesity raises blood pressure, worsens cholesterol levels, and increases inflammation throughout the body.
These factors rarely act alone. Someone with high blood pressure, elevated cholesterol, and a smoking habit faces a compounding risk far greater than any single factor would produce on its own.
Genetics and Inherited Risk
Some people inherit a higher baseline risk for heart attacks regardless of lifestyle. One important genetic factor is a blood particle called lipoprotein(a), or Lp(a). High levels run in families and are surprisingly common, affecting roughly one in five people at levels above 50 mg/dL. Unlike regular LDL cholesterol, Lp(a) levels are largely set by your genes and don’t respond much to diet or exercise.
Lp(a) raises heart attack risk through three separate mechanisms. It deposits cholesterol into artery walls just like LDL does. It promotes inflammation, which makes existing plaque more fragile and prone to rupturing. And it increases the blood’s tendency to clot, meaning that when a rupture does occur, the resulting blockage forms faster and can be more severe. If you have a strong family history of early heart attacks, Lp(a) is worth asking about, since it requires a specific blood test that isn’t part of a standard cholesterol panel.
Coronary Artery Spasms
Not every heart attack involves clogged arteries. A coronary artery spasm is a sudden, temporary tightening of one of the arteries that feeds the heart. During a spasm, the artery squeezes down so tightly that blood flow drops dramatically. A severe enough spasm can trigger a full heart attack even in arteries that are completely free of plaque.
Known triggers for coronary artery spasms include smoking, cocaine and amphetamine use, extreme emotional stress, and exposure to cold temperatures. This type of heart attack is sometimes called Prinzmetal’s angina or vasospastic angina, and it can strike people who appear otherwise healthy.
Spontaneous Coronary Artery Dissection
Spontaneous coronary artery dissection, or SCAD, occurs when the inner layers of a coronary artery tear apart. Blood seeps between the layers of the artery wall, creating a bulge that narrows or blocks blood flow. Unlike atherosclerosis, SCAD has nothing to do with cholesterol or plaque.
SCAD disproportionately affects young and middle-aged women who don’t have traditional heart disease risk factors. For years it was considered extremely rare, but enrollment in research programs has far outpaced expectations, suggesting SCAD is underdiagnosed rather than uncommon. Researchers at Mayo Clinic note that many SCAD patients are relatively healthy people who wouldn’t typically be screened for heart problems.
Inflammation as a Hidden Driver
Chronic, low-grade inflammation throughout the body plays a larger role in heart attacks than most people realize. Inflammation doesn’t just contribute to plaque formation. It actively destabilizes existing plaque, weakening the fibrous cap and making rupture more likely.
Doctors can measure systemic inflammation with a blood test for C-reactive protein, or CRP. Levels below 1 mg/L are considered low risk, 1 to 3 is intermediate, and above 3 is high. People with elevated CRP face greater heart attack risk even when their cholesterol numbers look normal, which is why inflammation is increasingly recognized as an independent threat rather than just a byproduct of other risk factors. Conditions like rheumatoid arthritis, lupus, and chronic gum disease all raise CRP levels and, with them, cardiovascular risk.
Sleep Apnea and Overnight Risk
Obstructive sleep apnea, where breathing repeatedly stops and restarts during sleep, is an underappreciated cause of heart attacks. Each time breathing pauses, blood oxygen levels drop. The brain forces a sudden awakening to restart breathing, which triggers a spike in blood pressure and heart rate. This cycle can repeat dozens or hundreds of times per night.
An NIH-funded study found that for every measured reduction in blood oxygen levels during sleep, heart attack and stroke risk increased by up to 45%. Over time, these nightly oxygen drops and blood pressure surges damage artery walls, promote inflammation, and accelerate atherosclerosis. Many people with sleep apnea don’t know they have it, which means the cardiovascular damage accumulates silently for years.
Acute Triggers That Set Off an Attack
In someone who already has vulnerable plaque, certain sudden stressors can be the final push. Intense physical exertion raises heart rate and blood pressure sharply, increasing the mechanical force on artery walls. This can crack a weakened fibrous cap, dislodge plaque debris, or trigger a spasm in a diseased artery segment. The body also releases stress hormones during extreme effort that make blood platelets stickier and more prone to clotting.
Extreme emotional stress works through a similar pathway. A surge of adrenaline raises blood pressure, speeds up the heart, and promotes clotting. This is why heart attacks sometimes cluster after natural disasters, major sporting events, or personal crises like the death of a loved one. The underlying disease was already there; the emotional event provided the trigger.
Cold weather is another acute trigger. Blood vessels constrict in cold air to preserve body heat, which raises blood pressure and can provoke spasms in already narrowed arteries. Heart attacks are more common in winter months for this reason.
Silent Heart Attacks
About one in four heart attacks produces no classic symptoms at all. These silent heart attacks cause the same damage to heart muscle, but the person may experience only mild discomfort, fatigue, or nothing noticeable. They’re often discovered later when an electrocardiogram picks up characteristic changes in heart rhythm patterns, or when imaging reveals scarred heart tissue.
Silent heart attacks are especially common in people with diabetes, likely because nerve damage from high blood sugar dulls the chest pain signals that would normally sound the alarm. Data from the long-running Framingham Heart Study showed that silent heart attacks carry a prognosis just as poor as symptomatic ones, making them particularly dangerous precisely because they go untreated. Up to one third of all heart attacks identified in diabetic patients through routine monitoring turned out to be ones the patient never felt.