Left ventricular function was studied before and after production of acute myocardial infarction by selective mercury embolization of the circumflex coronary artery in 8 closed chest dogs lightly anesthetized with morphine and chloralose. Ventricular function curves relating stroke volume, stroke work and mean stroke power to left ventricular end-diastolic pressure were determined. Stroke volume was obtained by an indicator dilution method with the heart rate kept constant by pacing. Left ventricular end-diastolic pressure was acutely increased by three 100 cc infusions of dextran before and 45 minutes after embolization. With dextran infusion before embolization, the mean right atrial pressure and the left ventricular end-diastolic pressure increased linearly; following embolization the left ventricular end-diastolic pressure increased out of proportion to the right atrial pressure. After embolization, the slope of the ventricular function curves was depressed consistently. However, the cardiac output post-embolization could be increased with dextran infusion up to a left ventricular Filling pressure of 19–20 mm Hg beyond which the curves relating output to filling pressure flattened or actually decreased. Thus, left ventricular function was measurably diminished following acute myocardial infarction in this experiment.