Heart beats that occur outside the heart's regular rhythm are known as "extrasystoles." They often arise in the ventricles, in which case they are referred to as "premature ventricular contractions" or sometimes "premature ventricular complexes," abbreviated as PVCs. The cause of such extra beats can be benign or can result from serious underlying heart disease. PVCs are common even in healthy individuals; they have been recorded in 75 percent of those who undergo prolonged cardiac monitoring (for at least 24 hours, that is). The incidence of PVCs also increases with age; they have been recorded in more than 5 percent of individuals more than 40 years old who undergo an electrocardiogram (or ECG, a test that typically takes less than 10 minutes to administer). Men seem to be affected more than women. The extrasystole itself is usually not felt. It is followed by a pause — a skipped beat — as the heart's electrical system resets itself. The contraction following the pause is usually more forceful than normal, and this beat is frequently perceived as a palpitation — an unusually rapid or intense beat. If extrasystoles are either sustained or combined with other rhythm abnormalities, affected individuals may also experience dizziness or lightheadedness. Heart palpitations and the sensation of missed or skipped beats are the most common complaints of those who seek medical care for extrasystole. [ad:media]A medical examination of the condition begins with a history and physical and should also include an ECG and various laboratory tests, including the levels of electrolytes (such as sodium, potassium and chloride) in the blood. In some cases, doctors may recommend an echocardiogram (an ultrasound examination of the heart), a stress test and/or the use of a Holter monitor (a device that records the heart's electrical activity continuously for a 24- to 48-hour period). Holter monitoring may uncover PVCs that are unifocal — that is, they originate from a single location. Of greater concern are multifocal PVCs — those that arise from multiple locations — as well as those that exhibit specific patterns known R-on-T phenomenon, bigeminy and trigeminy. If serious structural disorders, such as coronary artery disease or cardiomyopathy (a weakening of the heart muscle), can be ruled out — and the patient remains asymptomatic — the only "treatment" required may be reassurance. But for symptomatic patients, the course is less clear, as there is controversy regarding the effectiveness of the available treatment options. Two drugs commonly used to treat high blood pressure — beta blockers and calcium channel blockers — have been used in patients with extrasystole with some success. Antiarrhythmics have also been prescribed for extrasystole but have met with mixed reviews. A procedure known as cardiac ablation may be an option for symptomatic patients, if the location where their extra beats arise can be identified; the procedure involves threading tiny electrodes into the heart via catheters, then zapping the affected locations to rewire the heart's faulty circuits.