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.
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.