But a persistent irregular heartbeat can signal something more serious. The good news is that these conditions often respond well to treatment. It all depends on the kind of abnormal heart rhythm involved. Doctors will need to carry out tests to find out what's causing it before recommending treatment.

The heart of the problem, so to speak, is electrical. Heartbeats are triggered by electrical impulses that are generated within the heart itself. The signal is sent from the upper right chamber (sometimes called the heart's natural pacemaker) to the three other chambers of the heart. The two upper chambers (the atria) contract just before the two lower chambers (the ventricles). If everything is firing normally, the heart beats at a steady rate of somewhere between 60 and 100 times a minute.

When things don't function as they should, arrhythmia can be the result. Sometimes the electrical signal gets blocked; sometimes heart cells that aren't supposed to send out electrical signals try to assume the electrical pace setting and sometimes the signals don't follow the usual route.

What are the main kinds of arrhythmia?

Arrhythmia is the medical term that refers to a variety of abnormal heart rhythms caused by a change in the usual sequence of electrical impulses.

There are two main types: Bradycardia refers to a heart rate that is so slow, the person can't get enough blood to carry out everyday activities. Left untreated, it can lead to dizziness, lightheadedness or fainting and sometimes even death. How slow must a heart rate be before it's considered too slow? While a person's heart rate depends on their age and physical condition, some medical authorities say a heart rate of less than 60 beats a minute signals bradycardia.

Bradycardia can be caused by a variety of electrical malfunctions, including what's called "heart block." This doesn't refer to a physical blockage in an artery but to a problem in how the electrical signals are transmitted from the top two heart chambers to the lower two. Heart block is more common among the elderly, especially those with underlying heart problems.

Tachycardia, on the other hand, refers to a too-fast resting heart rate. What is too fast? Some set a rough barrier of more than 100 beats a minute. Some kinds of tachycardia are relatively benign and easily treated. Others are more serious and can be life-threatening.

There are two main kinds of tachycardia: supraventricular (which occur in the two upper chambers of the heart) and ventricular (which occur in the two lower chambers).

Supraventricular tachycardias can take many forms. An atrial flutter happens when the muscles in the top two chambers contract at a much higher heart rate than normal. Atrial flutter is usually not life threatening but can cause chest pain.

Atrial fibrillation (AF) is even more common than atrial flutter. With AF, the heart's upper chambers emit unco-ordinated electrical signals that cause the chambers to contract so quickly that blood isn't pumped effectively. While AF isn't life threatening in itself, a prolonged attack can lead to other serious problems, including stroke. According to one estimate, 15 to 20 per cent of all strokes occur in people with AF. The irregular heartbeat that sent Pittsburgh Penguins hockey star Mario Lemieux to hospital in December 2005 was diagnosed as atrial fibrillation.

Ventricular tachycardia is potentially fatal because it is the ventricles (the lower two heart chambers) that pump the blood to the rest of the body. Ventricular fibrillation involves the ventricles contracting in such a rapid-fire, unsynchronized way that little or no blood actually gets pumped. Without immediate medical treatment, victims of ventricular tachycardia or ventricular fibrillation can die.

When Detroit Red Wings hockey player Jiri Fischer collapsed on the bench in November 2005, doctors used a portable defibrillator device to deliver an electric shock to stabilize his heart and get his blood pumping again. The machine indicated that he was experiencing either ventricular tachycardia or ventricular fibrillation.

How is arrhythmia diagnosed and treated?

Diagnosis and treatment depend on what is causing the arrhythmia and what kind of arrhythmia it is. The standard way of pinpointing the nature of the problem is an electrocardiogram (ECG). Electrodes are placed on several parts of the body (it doesn't hurt) and a machine records the timing of the electrical signals in the various heart chambers. The size and shape of the electrical waves speak volumes about what's going wrong with one's ticker.

There are also small, portable ECG devices called Holter monitors than can record electrical activity over a longer period of time, say 24 hours. Wear it like a Walkman. The tape will be analyzed later for signs of arrhythmia.

Stress ECG tests, also called exercise ECGs, can be performed when a patient notices arrhythmia during exercise. Patients will be asked to walk or run while on a treadmill or ride a stationary bike while their heart is monitored.

People who faint repeatedly are often given a "tilt table" test to determine if the heart rate and blood pressure are affected by such things as sitting up or standing.

Electrophysiology studies may be called for when other tests fail to pinpoint the problem. The procedure, which has been described as slightly unpleasant but safe, involves the insertion of special catheters into a vein. Then they'll be guided into the right side of the heart. Doctors then stimulate the heart and can study the electrical response with more precision than with an ECG.

Treatment can run the gamut from nothing to major medical intervention. Sometimes a change in diet can be enough to fix the problem. Sometimes medications are prescribed to slow down a heart that's beating too fast. Beta-blocker drugs can also be used to treat tachycardia. Sometimes a change in heart medication can eliminate arrhythmia problems.

Sometimes a battery-operated artificial pacemaker needs to be implanted to regulate the heartbeat. Pacemakers, which deliver an electrical jolt when needed, can be very effective in treating an excessively slow heartbeat. Permanent pacemakers are implanted, usually under the collarbone. There are also implantable defibrillators for people in danger of having a deadly ventricular arrhythmia. And as an emergency measure, auto defibrillators can be used as a lifesaving measure.

Sources: Heart and Stroke Foundation of Canada, American Heart Association