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.
Heart attacks are caused by a build-up of fatty deposits in the arteries. These deposits are largely made up of LDL, or bad cholesterol, and they cause the arteries to become narrowed or blocked, cutting off the blood supply. The body's immune system tries to remove these fatty deposits, but goes into overdrive.