Each year, 1.1 million Americans experience a heart attack; 460 000 of them are fatal. Of those who die, almost half do so suddenly, before they can get to a hospital.  Not much bigger than a fist, the human heart beats 100,000 times each day, sending about 2,000 gallons of blood coursing through vessels, which, laid end-to-end, would be long enough to circle the earth more than twice.

To carry out the vital task of pumping blood, the electrical timing of millions of heart cells must be exquisitely coordinated. Their timing sparks the heart to pump in a rhythmic, efficient fashion. When that coordination is disrupted, life-threatening ventricular arrhythmias result.

Each heartbeat normally starts in the upper right chamber of the heart, or right atrium. Here, a specialized bunch of cells called the sinus node, or pacemaker, sends an electrical signal. The signal spreads throughout the right and left atria and then travels along specific pathways to the lower chambers or ventricles. As the signal travels, the heart muscle contracts. First the atria (the upper right and left chambers) contract, pumping blood into the ventricles. A fraction of a second later, the ventricles contract in a squeezing motion, sending blood throughout the body. Each contraction is a heartbeat.

Ventricular arrhythmias occur when a group of heart cells in the ventricles triggers contractions out of sync with the normal rhythm established by the sinus node. A number of factors can prompt a ventricular arrhythmia, including stress, exercise, caffeine, tobacco, alcohol, amphetamines, tricyclic antidepressant drugs, and cough and cold medicines containing pseudoephedrine, as well as several drugs (such as diuretics and digitalis) used to treat various heart conditions.

Many people think that heart attacks are a "man’s problem," yet heart disease is actually the number one killer of both men and women in the United States. In men, the risk for heart attack increases significantly after the age of 45. In women, heart attacks are more likely to occur in the years after menopause (usually, after the age of 50). However, younger men and women can also have heart attacks.

Besides age, factors that increase the risk for heart attack are:

• A previous heart attack or procedure to open up the coronary arteries
• Family history of early heart disease:
  • Father or brother diagnosed before age 55 
  • Mother or sister diagnosed before age 65
• Diabetes mellitus
• High blood cholesterol
• High blood pressure
• Cigarette smoking
• Overweight
• Physical inactivity

During a heart attack, a clot in the heart’s artery blocks the flow of blood to the heart. Heart muscle begins to die. This is technically called a "myocardial infarction," meaning "death of heart muscle." The more time that passes without treatment, the greater the damage. The part of the heart that dies during a heart attack cannot grow back or be repaired.

Many people think that a heart attack is sudden and intense, like the "Hollywood" heart attack depicted in the movies, where a person clutches his or her chest and falls over. The truth is that many heart attacks start as a mild discomfort in the center of the chest. Someone who feels such a warning may not be sure what is wrong. The discomfort (and other symptoms) may even come and go. Even people who have had a heart attack may not recognize the signs, because the next one can have entirely different symptoms. The warning signs of a heart attack are shown in the box below. Learn them, but also remember: Even if you’re not sure it’s a heart attack, you should still check it out promptly.

Heart Attack Warning Signs

• Chest discomfort. Most heart attacks involve discomfort in the center of the chest that lasts for more than a few minutes or that goes away and comes back. The discomfort can feel like uncomfortable pressure, squeezing, or fullness.
• Discomfort in other areas of the upper body. Symptoms can include discomfort in one or both arms or in the back, neck, jaw, or stomach.
• Shortness of breath. This symptom often accompanies chest discomfort. However, it can also occur before the chest discomfort.
• Cold sweat, nausea, or light-headednes.

Fortunately, clot-busting drugs and other artery-opening treatments, such as