Pre-Algebra on Khan Academy: No way, this isn't your run of the mill arithmetic. This is Pre-algebra. You're about to play with the professionals. Think of pre-algebra as a runway.
Coronary artery disease. The most common underlying cause of heart attack is atherosclerosis, a condition in which a fatty substance called plaque builds up on the inside walls of blood vessels. When this occurs in the coronary arteries, it's known as coronary artery disease (CAD).
A heart attack can be caused by many possible factors. Your heart muscle requires a steady supply of blood and oxygen. A heart attack occurs when that supply is interrupted or blocked. The release of a blood clot from hardened coronary arteries is often the culprit. Many illnesses, as well as drugs, especially cocaine and contraceptive pill usage, can cause a heart attack.