A heart attack, or myocardial infarction, occurs when a coronary artery (one of the arteries that supplies blood to the heart muscle) becomes suddenly blocked. The sudden blockage robs a portion of the heart muscle of its vital blood supply, and the muscle dies. So a heart attack is the death of a part of the heart muscle.
The sudden blockage of a coronary artery is usually caused by the rupture of a plaque in the artery. Plaque rupture can produce a variety of clinical conditions -- including heart attacks and unstable angina -- that are lumped together under the name acute coronary syndrome (ACS). All forms of ACS are medical emergencies, and they generally need to be treated with medications, angioplasty and stenting, or surgery to restore normal blood flow through the blocked artery. If blood flow can be restored within a few hours, permanent damage to the heart muscle can usually be minimized.
A cardiac arrest, in contrast, is caused by a sudden heart arrhythmia called ventricular fibrillation. In ventricular fibrillation, the electrical signals within the heart suddenly become completely chaotic. Because these electrical signals control the timing and the organization of the heartbeat, when those signals degenerate to total chaos, the heart suddenly stops beating. That is, it goes into "cardiac arrest." The most common outcome of a cardiac arrest is sudden death.
The treatment for a cardiac arrest is to begin immediate cardiopulmonary resuscitation (CPR) to support the victim's circulation, and, as soon as possible, to deliver a large electrical shock to the heart with a device called a "defibrillator." The large shock allows the heart's electrical signal to reorganize itself, and the heart starts beating again. Unfortunately, because death occurs within a few minutes of cardiac arrest unless expert help is available, the large majority of individuals who suffer cardiac arrest are not successfully resuscitated.
Cardiac arrest tends to be much more common in people who have various types of underlying heart disease -- most commonly, a prior heart attack or any condition that produces heart failure. Indeed, many patients who have had either a heart attack or heart failure ought to be considered for insertion of an implantable cardiac defibrillator, a device that automatically resuscitates people who suffer cardiac arrests. Other causes of cardiac arrest include certain inherited heart abnormalities that tend to increase the risk of ventricular fibrillation (the most common of these being hypertrophic cardiomyopathy) and the use of various illicit drugs (especially cocaine).
If a close relative has died, especially if suddenly, it is important to try to learn the precise cause of death. Your risk of heart attack, and of some types of cardiac arrest, may be higher if a close relative has experienced these events. Make sure you get as much information as you can. Ask the doctor to speak precisely to you about what actually happened.
Demirovic, J, Myerburg, RJ. Epidemiology of sudden coronary death: An overview. Prog Cardiovasc Dis 1994; 37:39.
Rea, TD, Pearce, RM, Raghunathan, TE, et al. Incidence of out-of-hospital cardiac arrest. Am J Cardiol 2004; 93:1455.