Regional cerebral blood flow (rCBF) was studied in anesthetized dogs subjected to acute left ventricular failure and its treatment with enalaprilat (MK-422). When failure was induced a reduction in rCBF paralleling the reduction in systemic blood pressure was observed. After treatment rCBF did not change in spite of further blood pressure reduction. The results are explained by changes in vascular resistance of larger cerebral arteries. Vasoconstriction in these vessels during failure was counteracted by enalaprilat through reduction in circulating angiotensin II.