Heart disease develops when the arteries supplying blood to your heart become narrowed, stiffened, or blocked by a buildup of fatty deposits called plaque. In the United States, someone has a heart attack every 40 seconds, and coronary heart disease killed 371,506 people in 2022 alone. The causes range from controllable factors like high blood pressure and cholesterol to inherited genetic traits you can’t change. Understanding what drives the process helps explain why roughly 1 in 20 adults over age 20 already have coronary artery disease.
How Plaque Builds Up in Your Arteries
Heart disease almost always starts with damage to the inner lining of your arteries, a thin layer of cells called the endothelium. When this lining is healthy, it keeps blood flowing smoothly and prevents cholesterol from seeping into the artery wall. When it’s damaged by high blood pressure, smoking, high blood sugar, or other stressors, it becomes leaky. Cholesterol-carrying particles in your blood, particularly LDL (“bad” cholesterol), slip through that damaged lining and get trapped inside the artery wall.
Once trapped, those LDL particles undergo chemical changes. They become oxidized, which triggers your immune system to treat them as a threat. White blood cells called monocytes migrate into the artery wall, transform into macrophages, and begin swallowing the modified cholesterol. These bloated immune cells become “foam cells,” and clusters of them form the earliest visible sign of heart disease: a fatty streak.
Over years or decades, smooth muscle cells in the artery wall multiply and produce a fibrous cap over the growing deposit. Beneath that cap sits a core of oxidized cholesterol, dead cells, and cellular debris. This is a mature plaque. It narrows the artery and restricts blood flow, but the real danger comes when the cap weakens and ruptures, exposing the core to your bloodstream and triggering a blood clot. That clot can block the artery entirely, causing a heart attack.
High Blood Pressure and Artery Damage
High blood pressure is one of the most potent drivers of heart disease because it physically damages your arteries from the inside. When blood pushes against artery walls with sustained force, the cells lining those walls change their behavior. They begin producing signals that thicken the artery wall, stiffen it, and attract immune cells. The 2025 guidelines from the American Heart Association classify blood pressure of 130/80 or higher as hypertension, with a treatment goal of keeping readings below that threshold.
The damage from high blood pressure creates a destructive feedback loop. As artery walls thicken and stiffen in response to excess pressure, the increased stiffness itself drives more inflammation. Immune cells respond to the rigid environment by releasing compounds that remodel the wall further, locking in a stiffer structure that provokes even more immune activity. Over time, this leads to scarring in the outer layers of the artery, reducing the vessel’s ability to expand and contract normally. The result is an artery that’s both structurally compromised and more hospitable to plaque formation.
Cholesterol’s Central Role
LDL cholesterol doesn’t just passively drift into artery walls. It’s actively transported across the endothelial lining through specific cellular channels. Tiny flask-shaped pockets on the surface of endothelial cells grab LDL particles and shuttle them through to the other side. This transport process is a normal part of biology, but when LDL levels are high or the endothelium is damaged, far more particles cross than the body can clear.
The smaller and denser the LDL particle, the more dangerous it tends to be. Small, dense LDL particles penetrate artery walls more easily, resist the body’s normal cholesterol-clearing mechanisms, linger in the bloodstream longer, and are more susceptible to oxidation. Once oxidized, LDL binds to receptors on endothelial cells that impair the artery’s ability to relax, promote the sticking of immune cells to the artery wall, and push the lining toward a clot-friendly state.
Inflammation Turns Stable Plaques Dangerous
A plaque can sit in an artery wall for years, gradually narrowing blood flow without causing a heart attack. What makes it dangerous is inflammation. When immune cells inside the plaque become heavily activated, they release enzymes that systematically dismantle the fibrous cap holding the plaque together. One group of enzymes breaks down collagen fibers, another degrades the fragments, and still others dissolve the elastic tissue that gives the cap its structural integrity.
At the same time, a specific type of immune signaling molecule released by activated T cells nearly shuts down new collagen production, so the cap can’t repair itself. The result is a thinning, weakened cap over a growing necrotic core. When macrophages inside the plaque die in large numbers, their remains accumulate because the body’s cleanup system becomes impaired in advanced disease. This swelling necrotic core pushes against the thinning cap from below. Pathology studies of ruptured plaques consistently find large numbers of macrophages, peak T cell counts, thinning caps, and networks of fragile new blood vessels at the rupture site.
Insulin Resistance and Blood Sugar
Insulin resistance, the condition underlying type 2 diabetes and prediabetes, damages arteries through several overlapping pathways. Normally, insulin helps blood vessels relax by stimulating the production of nitric oxide, a molecule that signals artery walls to widen. When cells become resistant to insulin, this protective signaling weakens. Instead, insulin activates an alternative pathway that promotes smooth muscle cell growth, inflammation, and plaque buildup.
Insulin resistance also distorts your cholesterol profile in ways that standard tests may not fully capture. When insulin can’t do its job in the liver, the liver overproduces triglyceride-rich particles, which leads to higher levels of small, dense LDL, the most damaging form. These particles enter artery walls more easily and oxidize more readily. On top of that, chronically elevated blood sugar causes proteins and fats throughout the body to become chemically modified by glucose, forming compounds that generate oxidative stress and further damage the artery lining. This is why people with diabetes face heart disease risk that goes well beyond what their cholesterol numbers alone would suggest.
Smoking’s Direct Attack on Blood Vessels
Smoking damages arteries through both immediate chemical effects and long-term structural changes. The chemicals in cigarette smoke reduce the availability of nitric oxide, the same protective molecule that insulin resistance impairs. With less nitric oxide, arteries lose their ability to relax properly, and the endothelial lining begins expressing sticky surface molecules that attract immune cells.
This sets off the same cascade that drives plaque formation. Platelets and macrophages adhere to the damaged lining, creating a pro-inflammatory, clot-friendly environment. Macrophages migrate into the artery wall, engulf oxidized LDL, and become foam cells. Smoking also accelerates the oxidation of LDL in the bloodstream, providing more fuel for this process. Beyond the direct vascular damage, smoking triggers body-wide inflammatory signals that compound the local effects in the arteries. The combination of physical endothelial damage, reduced nitric oxide, increased oxidation, and systemic inflammation makes smoking one of the most efficient accelerators of heart disease.
Genetic Risk You Can’t Control
Some people develop heart disease despite having textbook-healthy habits. One major reason is lipoprotein(a), often written as Lp(a), a cholesterol particle whose levels are 70% to 90% determined by your genes. Unlike standard LDL, Lp(a) barely responds to diet, exercise, or even most cholesterol-lowering medications including statins. Large genetic studies have confirmed that elevated Lp(a) is an independent causal factor for cardiovascular disease, meaning it increases your risk regardless of your other cholesterol numbers.
Lp(a) is particularly concerning because it can drive heart disease even when LDL cholesterol is within the recommended range. This is sometimes called “residual cardiovascular risk,” the portion of heart disease risk that persists after all the standard numbers look good. Most people have never had their Lp(a) tested because it isn’t part of a routine lipid panel, but a single lifetime measurement can reveal whether you carry this genetic risk factor.
How Heart Disease Differs in Women
Heart disease is the leading cause of death in women, but it often looks different than it does in men. Women are more likely to develop problems in the tiny blood vessels that branch off the main coronary arteries, a condition called coronary microvascular dysfunction. Up to 50% of women who undergo cardiac catheterization for chest pain have normal or near-normal main arteries but show clear signs of reduced blood flow in these smaller vessels.
The causes of microvascular dysfunction include an imbalance between molecules that relax blood vessels and those that constrict them, with women showing lower levels of the relaxing signal (nitric oxide) and higher levels of the constricting one. Heightened activity in the nerves that control heart vessel tone also plays a role, with about 75% of patients in one study showing overactive cardiac nerve signaling. Women with this condition are typically in the perimenopausal or menopausal stage of life, with symptoms usually starting between ages 40 and 50. Because standard cardiac testing focuses on blockages in large arteries, microvascular dysfunction is frequently missed, leading to delayed diagnosis and treatment.
How These Causes Overlap
Heart disease rarely has a single cause. High blood pressure damages the artery lining, making it easier for LDL to penetrate. Insulin resistance floods the bloodstream with small, dense LDL while simultaneously impairing the artery’s ability to protect itself. Smoking accelerates oxidation of the cholesterol already accumulating in artery walls. Inflammation, whether driven by metabolic dysfunction, high blood pressure, or immune activation within plaques, amplifies every other risk factor by promoting plaque growth and instability.
This is why heart disease prevention focuses on managing multiple risks simultaneously rather than fixating on a single number. Blood pressure below 130/80, LDL cholesterol kept low (particularly in people with existing risk factors), blood sugar under control, no smoking, and awareness of genetic factors like Lp(a) all work together to slow or prevent the chain of events that leads from a healthy artery to a heart attack. About 805,000 Americans have a heart attack each year, and 200,000 of those are in people who have already had one, reinforcing that the underlying causes persist unless actively addressed.