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.
Heart attack - Causes. Heart attacks are caused by the blood supply to the heart being suddenly interrupted. Without this supply, heart muscles may be damaged and begin to die. Without treatment, the heart muscles will experience irreversible damage.
A heart attack is commonly caused by a blockage of the coronary artery. Cholesterol in the form of plaque builds up on the inside wall of the coronary artery. Over time, plaque accumulation can narrow the artery, reducing blood flow to the heart.