The effects of coronary artery ligation on regional arterial and venous O2 saturation, oxygen extraction, blood flow, and oxygen consumption were studied in occluded and unoccluded areas of the hearts of fourteen anesthetized open-chest dogs. In seven animals, a coronary artery was occluded for 10 minutes and in seven others a vessel was ligated for 2 hours. Microspectrophotometric observations of small regional arteries and veins in quick-frozen hearts to determine regional O2extraction were combined with regional blood flow measurements with radioactive microspheres to determine regional myocardial O2 consumption by the Fick principle. Flow was significantly lower in the occluded compared to the control area at both times. The subendocardial: subepicardial flow ratio was reversed at 2 hours in the occluded area. Oxygen extraction was greater in the occluded areas. Oxygen consumption was lower in the occluded area. At 2 hours, the subendocardial: subepicardial consumption ratio was reversed in the occluded area, indicating a greater decrement in consumption in the subendocardium. Measurements of arterial saturation indicate an increasing number of blood vessels with O2 saturations below 80% with coronary artery occlusion. These vessels were found in all occluded areas. This would indicate a marked heterogeneity of blood flow within the area of occlusion. Some vessels may have normal flow and others low or no flow. There was heterogeneity of flow and oxygen extraction which led to areas with relatively normal oxygen consumption in the core of the infarct.CircRes 47: 400-407, 1980