The  heart is an amazing organ.  It is a muscle, it is a pump, and it is an "appliance" that is controlled by electical impulses and by chemical substances in the body.  When the heart muscle dies, death occurs if the heart is not replaced. 

Heart death can occur quickly, during a heart attack.  When the arteries that feed the he heart muscle with oxygen rich blood are blocked, all or a portion of the heart muscle dies.

The heart can also die slowly.  The heart muscle can lose its ability to pump, either from disease or from a gradual deterioration of the heart muscle from hardening of the arteries.  If hardening of the arteries occurs, the heart muscle may not be able to keep pace with the increased demands to pump faster to maintain blood flow.

Eventually in this situation, heart failure occurs.  Ff the heart muscle is not assisted with mechanical devices such as an electrical pacemaker to maintain the heart rhythm, or devices such as heart pumps, death occurs if the heart is not replaced.

Proper diet, exercise and cholesterol control can reduce the risk of heart failure.