Antihypertensive management reduces the incidence of congestive heart failure, malignant hypertension and stroke; however, the overall incidence of events due to ischemic heart disease was not influenced by antihypertensive treatment. One of the possible explanations might be some negative metabolic effects of antihypertensive drugs. Hypokalemia develops in 20 to 50% patients who receive a thiazide diuretic. An association between hypokalemia and malignant arrhythmias (including ventricular fibrillation), in acute myocardial infarction, has been observed. 24-hour ambulatory electrocardiographic monitoring demonstrated a higher frequency of ventricular ectopic beats in hypertensive patients taking thiazides. There is, however, no convincing evidence of a simple causative relation between ventricular extrasystoles and low concentrations of serum potassium. Hypertensives with left ventricular hypertrophy (ECG criteria) had significantly more premature ventricular contractions than patients with established hypertension without left ventricular hypertrophy or normotensive subjects. These data could provide an electrophysiologic substrate for the epidemiologic findings of increased morbidity and mortality in patients with left ventricular hypertrophy.