A heart attack can occur when the blood flow that provides oxygen to the heart muscle is severely reduced or completely blocked. This can happen because arteries that supply the heart with blood gradually become thicker and harder due to the buildup of fat, cholesterol, and other substances (also called plaque). *
If the plaque breaks loose, a blood clot can form, reducing or blocking blood flow: This is a heart attack.
* This slow process is called atherosclerosis.