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).
As time goes on, less and less oxygen makes it to the heart, which can cause a heart attack. Coronary artery disease can lead to heart failure and arrhythmias (irregular heart beats). While some people are genetically predisposed to heart disease, it often develops due to poor lifestyle habits.