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The effect of intravenous i.v. nifedipine 5 μgkgmin on regional O2supplyconsumption variables was determined in 14 anesthetized openchest dogs subjected to left anterior descending coronary artery LAD stenosis sufficient to reduce blood flow 50. Myocardial blood flow was measured using radioactive microspheres, and regional arterial and venous O2saturations were determined using microspectrophotometry. During LAD occlusion, blood flow and O2consumption were decreased in the ischemic region while O2extraction was increased. With nifedipine treatment, LAD flow flow probe was increased 44 as compared with the initial occluded value, with most of this increase going to the subepicardium microspheres. Flow to the ischemic subendocardium was not changed with nifedipine treatment. Ischemic subepicardial O2consumption increased slightly in nifedipinetreated animals as compared with saline values, whereas O2extraction decreased slightly. In the subendocardial region, nifedipine resulted in a significant decrease in O2extraction, with a slight decrease in O2consumption as compared with saline controls. The O2supplydemand ratio was significantly improved with nifedipine only in the subendocardium of the ischemic region. This suggested that nifedipine could increase O2consumption in the ischemic subepicardium through proportional increase in O2supply while it decreased O2consumption in the subendocardium relative to O2supply.