Endothelin (ET) is increased in plasma after myocardial infarction. Whether brief periods of myocardial ischemia not leading to myocardial infarction also increase plasma ET is not known. The purpose of the present study was to examine cardiac ET balance in association with a 10-min LAD occlusion followed by reperfusion. Venous blood was selectively sampled from the transiently ischemic myocardium using a shunt between the anterior interventricular vein and the right atrium in eight pentobarbital-anesthetized pigs. Flow in the shunt was measured with a Doppler flow probe. Arterial blood was drawn from the aortic arch. Plasma ET was measured using an ET [1-21]-specific 125I assay system. This assay system has no cross-reactivity with big ET. A net cardiac ET uptake of 0.7 (0.3-1.4) fmol min-1 g-1 (median, 95% confidence interval) in the control period shifted to a net release during the first 10 min of reperfusion. The release reached a maximum of 2.8 (0.4-6.0) fmol min-1 g-1 after 1.5 min of reperfusion. Cardiac venous ET concentration increased from 3.4 (2.5-4.8) to 4.4 (3.6-6.9) and 4.4 (3.6-6.6) fmol ml-1 at 1.5 and 5 min of reperfusion, respectively (p < 0.001 for both). Arterial ET concentration decreased from 4.8 (3.9-6.1) to 2.7 (2.4-4.3) fmol ml-1 at 10 min of reperfusion (p < 0.001). ET is released from the porcine heart for several minutes during reperfusion after a brief coronary artery occlusion.