What happens if your heart fails?

Heart failure: Heart failure means the heart is not pumping adequate output to satisfy the bodies needs. Usually this results in fluid retention, fatigue, edema, and shortness of breath. There is a form called diastolic failure in which the heart pumps adequately but to do this requires high intracranial pressures and fluid retention.

Depends: What do you mean fails. If the heart arrests, you are dead. If you mean congestive heart failure, then the fluid backs up in the tissues, the persons energy declines, the tissues suffer from hypo perfusion. The lungs become wet with fluid and the legs swell up.