The purpose of this study was to determine the effects of endothelin-1 on the coronary vascular bed of closed chest pigs. Endothelin-1 (3 to 30 pmol/kg body weight) was selectively administered into the left anterior descending coronary artery. Coronary blood flow and epicardial vessel diameter were measured by quantitative arteriography. Arterial pressure increased after a 30 pmol/kg dose and heart rate was not changed. Coronary blood flow and vessel diameter of the left anterior descending artery significantly decreased by 74% and 32%, respectively (p less than 0.01 versus control) after the 30 pmol/kg dose, whereas these variables modestly decreased in the left circumflex artery. Endothelin-1 in doses of 10 to 30 pmol/kg produced electrocardiographic ST segment elevation associated with decreased oxygen saturation of coronary sinus venous blood. Endothelin-induced coronary vasoconstriction was significantly inhibited after treatment with intravenous diltiazem (0.2 mg/kg, n = 6) or nifedipine (0.1 mg/kg, n = 5), but not after vehicle administration (n = 4). This study demonstrates that intracoronary administration of endothelin-1 causes significant myocardial ischemia through coronary vasoconstriction, which is inhibited by a calcium channel blocker. The data suggest that calcium influx into the smooth muscle cells appears to be involved at least in part in the mechanism of endothelin-induced coronary vasoconstriction in vivo.