1. The effects of coronary artery occlusion and reperfusion on pressure-induced changes in coronary blood flow and blood volume were investigated. 2. The left anterior descending coronary artery (LAD) of canine hearts was cannulated and perfused independently with arterial blood by a controlled pressure system. LAD flow was measured continuously with an electromagnetic flowmeter and LAD volume was measured in the steady-state by indicator dilution. Measurements were made with perfusion pressure at 100 mmHg (control), 50 mmHg, and 150 mmHg before and after 2 h of LAD occlusion followed by 2 h of reperfusion. 3. With perfusion pressure at control, occlusion-reperfusion reduced LAD flow 19%, but had no significant effect on LAD volume. 4. Steady-state LAD flow and volume always varied directly with changes in perfusion pressure; after occlusion-reperfusion these variations were accentuated. 5. Analysis of transient and steady-state flow responses indicated diminished capability of arteriolar resistance vessels for active, autoregulatory adjustments in lumenal calibre following changes in perfusion pressure. 6. The results of this study demonstrate that occlusion-reperfusion causes derangement to pressure-volume and pressure-flow control mechanisms in the coronary circulation.