Tiapamil (also known as Ro 11-1781) is a dithiane derivative patented by Hoffmann-La Roche, F., und Co., A.-G. as calcium-channel antagonist useful for myocardial infarction treatment. Tiapamil, like verapamil, inhibited in a concentration-dependent manner Ca2+-induced contractions in isolated, K+-depolarized preparations of rat renal artery, dog coronary artery and rabbit main pulmonary artery. The inhibitory effects of Tiapamil can be overcome by raising the Ca2+ concentration of the bath fluid. In the rabbit main pulmonary artery, Tiapamil reduces 45Ca influx into the K+-depolarized vascular smooth muscle cells. Tiapamil inhibits the slow potentials in partially depolarized guinea-pig papillary muscles. Tiapamil decreases contractile force in isolated guinea-pig atria and papillary muscles, as well as in isolated cat hearts. Tiapamil also reduces heart rate and increases coronary flow in these preparations. Tiapamil doubled coronary artery blood flow in the coronary sinus blood without producing major changes in blood pressure and heart rate in anesthetized dogs. Tiapamil did not affect contractions of isolated guinea-pig ileum, rat stomach strips or rat vas deferens in response to various stimulants. Tiapamil have no major effects on renal water and electrolyte excretion, on autonomic nerves and receptors, on pain perception and on the central nervous system. Acute, subacute, and chronic toxicity studies demonstrate low toxicity for Tiapamil with no tendency for accumulation. In clinical trials, Tiapamil effectively lowers systolic and diastolic blood pressure, but have no effects on heart rate