What's an irregular heartbeat?

Think for a minute about what keeps your heart going, beat after beat (the answer is not George Clooney). Yes, it needs a constant blood supply (that's why those smooth artery walls are so important), but it also needs the crucial electrical impulse that makes it beat steadily an average of 3.3 billion times in your life.

Normally, pacemaker cells living in the sinoatrial node of the atrium control the heartbeat, and the message is carried by a precious set of cables throughout the heart so it contracts on command in unison. If rogue groups of cells start making pacemaking decisions, or another electrical pathway becomes more dominant (for example, if the original path is damaged), then the heart rate becomes irregular.

Irregular heartbeats come in two forms: the kind that kill you (usually ventricular) and the kind that don't (usually originating above the ventricle or supreventricular, such as atrial fibrillation).

Not surprisingly, the same lifestyle factors that can lead to heart attacks also can lead to an irregular or erratic heart rhythm, known as an arrhythmia.

Irregular heartbeats are of two types: life-threatening and harmless. Almost everyone has an occasional "skipped beat," which is harmless. (Actually, "skipped beats" are usually extra or premature beats.) An electrocardiogram helps a doctor figure out if a person is having irregular heartbeats that may be dangerous. The most dangerous type is called ventricular fibrillation.