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).
The main event of a heart attack is the occlusion by a sudden blood clot of one or more blood vessels supplying the heart muscle. A similar occlusion of blood vessels supplying the brain will result in the death of brain tissue or cerebral infarction. Another cause of stroke is hemorrhage from a ruptured blood vessel.