The most common condition that predisposes a person to heart attack is underlying coronary artery disease that is caused due to the deposition of cholesterol and calcium along the walls of the coronary arteries. The arterial wall become thick and irregular due to build of these deposits called plaques and this process is called atherosclerosis.
The plaques along with blood clots block the artery partially or completely leading to insufficient blood supply to the heart muscle. This leads to lack of oxygen supply to the heart muscle in the affected area and if the blood supply is cut off long enough the heart muscle dies leading to heart attack.
The major disorders caused due to the insufficient blood supply are angina pectoris, congestive heart failure (CHF) and heart attack. These disorders are collectively known as coronary artery disease (CAD). Heart attack is the end point of coronary artery disease.
Coronary artery spasms or hemorrhage into a plaque may also lead to occlusion of the arteries, but these are less common causes of heart attack.