Leukotrienes C4 and D4 (LTC4 and LTD4), possible mediators of cardiac dysfunction during inflammatory injury, may depress cardiac function by reducing coronary flow or by exerting a negative effect directly on the myocardium. We used an isovolumic rat heart preparation perfused at constant pressure and measured left ventricular developed pressure (mmHg), coronary flow (ml.min-1), oxygen extraction, and myocardial oxygen consumption and delivery (mumol O2.[gramme dry weight]-1.min-1) during infusion of five doses of angiotensin II, LTC4, LTD4 (approximately 10 to approximately 300 pmol.min-1), and noradrenaline (400 to 2000 pmol.min-1), or perfusion with medium which contained calcium at half-concentration. LTC4 and LTD4 were equipotent with angiotensin. At low effective doses, increased oxygen extraction offset the decrease in oxygen delivery, maintaining a stable level of oxygen consumption and left ventricular developed pressure. At the highest doses, angiotensin, LTC4 and LTD4 reduced coronary flow from 21 to 15, 21 to 13, and 21 to 13 ml.min-1, respectively. And, despite greater oxygen extraction of 59%, 58% and 65% for angiotensin, LTC4 and LTD4, left ventricular developed pressure fell from a baseline of 120 mmHg to 113, 106 and 92, respectively. In contrast, low calcium perfusion reduced left ventricular developed pressure (126 to 92) and oxygen extraction (46 to 30%) without changing coronary flow or oxygen delivery. These results suggest that LTC4 and LTD4 are potent coronary vasoconstricting agents which depress cardiac function by limiting oxygen delivery.