Mild, isolated disturbances of this sort are normally harmless. A recurrent arrhythmia, on the other hand, should be checked by a physician. At rest, the heart beats somewhere between 60 and 100 times per minute. Tachycardia is defined as more than 100 beats per minute, while bradycardia is defined as fewer than 60 beats per minute. Both tachycardia and bradycardia can occur in surges or as persistent conditions.
Most arrhythmias fall into the tachycardia category.
Some originate in the atria, some in the ventricles. Ventricular arrhythmias are typically more serious conditions. In fact, most cases of sudden cardiac death are due to ventricular arrhythmias, not heart attack, as was once thought. Particularly dangerous is ventricular fibrillation, in which activity within the ventricles is so uncoordinated that the ventricles are reduced to twitching, and virtually no pumping takes place. Ventricular fibrillation will cause death within a few minutes unless treated with CPR and defibrillation as soon as possible.