a lot of things that cause heart attack
1. coronary arteries are blocked -- so blood is not able to travel to the heart muscle
2. too much water/fluids in the body -- makes it harder for the heart to pump
3. vascular (blood vessels) problems -- due to smoking
and other factors -- the blood vessels constrict, also harder for the heart to pump blood through narrowed vessels.
4. blockage in the vessels -- constricts the opening
imagine that you are a water pump -- when you are pumping water through narrowed openings, or you are pumping water twice more than you usually pump -- you get tired and you give up -- that's how the heart works.