Well the heart is like a house, it has the rooms, doors, wiring and plumbing. We can liken the rooms to the four chambers of the heart (atria and ventricles). The doors we can liken to the four valves that separate each chamber, the wiring we can like to how the heart electrical system initiates a contraction and finally, the plumbing we can liken to heart arteries that both feed oxygen and nutrients and just as important, take away metabolic waste products. Each one of these can go wrong, but primarily in a heart attack, the toilet gets stuffed up. What I mean is that a pipe/artery gets clogged and ALL the muscle downstream runs out of oxygen, waste products build up and the muscle tissue dies and becomes a scar. The higher up or closer to the origin of the artery from the aorta, the more severe it is as there is more muscle downstream. If that was the only thing to it, many people just have a section of muscle die and move on with diminished pump function. Unfortunately, when muscle dies it also kills off part off the wiring of the heart. This can lead to loops of electricity, an electrical dragon chasing it s tail. A swirl of electricity that leads to no cooridinated contraction. The heart fibrillates or just sort twitches madly. Therefore no flow goes forward and the brain and body die. So in one sense we can separate a plumbing heart attack and an electrical heart attack. Both can occur independent of the other. But if you have a plumbing heart attack, the electrical heart attack can occur as a result. An electrical heart attack is called sudden cardiac death it can occur in young people, middle age people and of course in old people. There are ion channels and a whole host of reasons why rarely people just go into an electrical meltdown of the heart. It is the most severe occurence as in the vast majority will die from it. That is why there is a push to have defibrillators in many public places. The defibrillator shocks the heart making all cells depolarize and then hopefully start uniformly contract and a heart contraction is actually useful to keep the blood moving. Hope that helps