Coronary heart disease develops when fatty deposits called plaques build up inside the arteries that supply blood to your heart. This process, called atherosclerosis, unfolds over decades and involves a combination of cholesterol buildup, inflammation, blood pressure damage, and lifestyle factors. It is the most common type of heart disease, killing 371,506 people in the United States in 2022 alone. About 1 in 20 American adults age 20 and older currently live with it.
No single cause is responsible. Coronary heart disease results from multiple forces acting on your blood vessels simultaneously, some within your control and some determined by genetics.
How Plaque Builds Up in Your Arteries
Your coronary arteries are lined with a thin layer of cells called the endothelium. This lining does more than act as a barrier. It actively regulates blood flow by producing a molecule called nitric oxide, which keeps arteries relaxed and open, prevents blood cells from clumping together, and stops artery walls from thickening. When this lining is healthy, blood flows smoothly and plaque has difficulty gaining a foothold.
The trouble starts when something damages the endothelium. High blood pressure, smoking, high blood sugar, or oxidized cholesterol particles can all injure it. Once damaged, the lining becomes more permeable, allowing LDL cholesterol to seep into the artery wall beneath it. There, LDL particles undergo chemical changes (oxidation) that trigger an immune response. White blood cells rush in to absorb the cholesterol, but they become engorged and form what pathologists call “foam cells,” the earliest visible sign of plaque.
Over time, smooth muscle cells in the artery wall multiply and migrate into the growing deposit. The plaque develops a core of fatty debris capped by a fibrous layer. Some plaques grow large enough to physically narrow the artery, restricting blood flow to the heart muscle. Others remain relatively small but become unstable, with thin caps less than 65 micrometers thick that can rupture without warning. When a plaque ruptures, a blood clot forms at the site and can block the artery entirely, causing a heart attack.
High Cholesterol and Oxidized LDL
LDL cholesterol is the primary raw material for plaque. The more LDL circulating in your blood, the more likely it is to penetrate artery walls. Optimal LDL is below 100 mg/dL. Levels between 130 and 159 mg/dL are considered borderline high, 160 to 189 mg/dL is high, and anything at or above 190 mg/dL is very high.
But the total number only tells part of the story. LDL becomes especially dangerous once it’s oxidized, a process accelerated by smoking, inflammation, and high blood sugar. Oxidized LDL directly suppresses nitric oxide production in artery walls by interfering with the enzyme that makes it. With less nitric oxide available, arteries lose their ability to relax and protect themselves. This creates a vicious cycle: damaged arteries let in more cholesterol, which causes more damage, which lets in still more cholesterol.
High Blood Pressure Damages Artery Walls
Every heartbeat pushes blood against your artery walls, creating mechanical stress. At normal pressures, this force is manageable and even necessary to keep vessel cells healthy. But chronically elevated pressure stretches and strains the artery wall beyond its comfort zone. The cells respond by thickening, stiffening, and producing extra structural proteins like fibronectin. In smaller arteries, the muscle cells multiply. In larger arteries, they enlarge. Both responses make the vessels less flexible and more prone to damage.
This remodeling process narrows the internal space of the artery and makes the endothelial lining more vulnerable to injury. High blood pressure also increases the turbulence of blood flow at branch points in the coronary arteries, which are already hotspots for plaque formation. The physical pounding acts as a constant accelerant for atherosclerosis, which is why hypertension is one of the strongest risk factors for coronary heart disease even in people with normal cholesterol.
Chronic Inflammation and Plaque Instability
Atherosclerosis is fundamentally an inflammatory disease. The immune system treats cholesterol deposits in the artery wall as foreign invaders and mounts a sustained inflammatory response. This inflammation doesn’t just contribute to plaque growth. It determines whether a plaque stays stable or becomes the kind that ruptures and causes a heart attack.
One marker of this process is C-reactive protein (CRP), a substance the liver produces in response to inflammation. People with the highest CRP levels face 1.5 to 7 times the risk of developing symptomatic atherosclerosis compared to those with low levels. Levels above 3.0 micrograms per milliliter are considered elevated. In studies of people who died from sudden cardiac events, those with acutely ruptured plaques had a median CRP of 3.2, while control subjects without coronary disease averaged 1.4.
Inside the plaques themselves, CRP deposits are heavier and macrophage infiltration is denser in people with elevated blood CRP. These immune cells weaken the fibrous cap that holds the plaque together, making rupture more likely. Inflammation, in other words, is what turns a stable, slowly growing plaque into a ticking time bomb.
Smoking and Nicotine
Smoking attacks coronary arteries from multiple directions at once. Nicotine activates your sympathetic nervous system, raising heart rate, blood pressure, and the force of each heartbeat. All of this increases how much oxygen your heart muscle demands. At the same time, carbon monoxide from cigarette smoke reduces the oxygen available in your blood, creating a dangerous mismatch between supply and demand.
Nicotine also causes coronary arteries to constrict, particularly in segments where the endothelial lining is already damaged. This raises the risk of vasospasm, a sudden tightening of the artery that can temporarily cut off blood flow even without a complete blockage. For someone who already has plaque buildup, a spasm in the wrong spot can trigger a heart attack. These effects aren’t limited to traditional cigarettes. Any nicotine delivery system, including e-cigarettes, activates the same sympathetic pathways and causes endothelial dysfunction.
Diabetes and High Blood Sugar
People with diabetes develop coronary heart disease at significantly higher rates and at younger ages. When blood sugar stays elevated over time, it damages the endothelial lining through several mechanisms. Excess glucose promotes oxidative stress, which depletes the same nitric oxide that keeps arteries healthy. High blood sugar also makes LDL particles more susceptible to oxidation and increases the stickiness of blood cells, promoting clot formation.
Insulin resistance, the metabolic problem underlying type 2 diabetes, compounds these effects. It shifts the body’s metabolism toward higher triglycerides, lower HDL (protective cholesterol), and the production of small, dense LDL particles that penetrate artery walls more easily than larger ones. This combination means even diabetic patients with “normal” total cholesterol numbers can have aggressive plaque buildup.
Physical Inactivity
A sedentary lifestyle accelerates coronary heart disease through the same endothelial pathway that other risk factors exploit. When you’re inactive for prolonged periods, your body produces more reactive oxygen species (unstable molecules that cause cellular damage) without the antioxidant defenses to neutralize them. This imbalance disrupts the enzyme responsible for making nitric oxide, reducing the amount available to keep arteries relaxed and protected. The result mirrors what happens with high cholesterol or high blood pressure: a vulnerable endothelium that lets plaque take hold.
Regular physical activity reverses this pattern by boosting nitric oxide production, reducing inflammation, improving cholesterol profiles, and lowering blood pressure. The protective effect is dose-dependent, meaning more activity generally provides more benefit, but even moderate amounts make a measurable difference in vascular function.
Genetics and Family History
Some people inherit a higher baseline risk for coronary heart disease regardless of how well they manage other factors. One of the clearest genetic contributors is lipoprotein(a), a cholesterol particle whose blood levels are almost entirely determined by your DNA. Unlike standard LDL, you can’t significantly change lipoprotein(a) through diet or exercise.
Risk thresholds are well established. Levels below 75 nmol/L are considered low risk, 75 to 125 nmol/L falls into a gray zone, and anything at or above 125 nmol/L (roughly 50 mg/dL) places you in the high-risk category. People in that top range need more aggressive management of every other risk factor they can control: cholesterol, blood pressure, weight, and physical activity. A family history of heart disease before age 55 in a father or brother, or before age 65 in a mother or sister, is a practical signal that genetic factors may be at play.
How Doctors Detect Early Disease
Because plaque can build up for decades before symptoms appear, screening tools help identify disease before a heart attack occurs. One of the most informative is a coronary calcium scan, a quick CT scan that detects calcified plaque in your coronary arteries and produces a numerical score.
- Score of 0: No calcium detected. This suggests a low chance of heart attack in the coming years.
- Score of 100 to 300: Moderate plaque deposits. This range carries a relatively high risk of a heart attack or other cardiac event within 3 to 5 years.
- Score above 300: More extensive disease with a higher heart attack risk.
A calcium score doesn’t capture every type of dangerous plaque, since soft, non-calcified plaques can also rupture. But a score of zero is powerfully reassuring, and a high score can motivate the kind of lifestyle changes and medical treatment that slow or stop progression. Your doctor may also assess risk through blood lipid panels, blood pressure readings, CRP levels, and lipoprotein(a) testing, especially if you have a strong family history.