Experiments were undertaken using rubidium-82 and position tomography to examine the relation between myocardial perfusion and cation uptake during acute ischemia. Rubidium-82 was repeatedly eluted from a strontium-82-rubidium-82 generator. In six dogs emission tomograms were used to measure the delivered arterial and myocardial concentrations at rest and after coronary stenosis, stress and ischemia. There was a poor overall relation between regional myocardial uptake and flow measured by microspheres and a large individual variability. Extraction of rubidium-82 was inversely related to flow. Significant regional reduction of cation uptake was detected in the tomograms when regional flow decreased by more than 35 percent. This reduction was significantly greater when ischemia was present. A small but significantly greater when ischemia was present. A small but significant decrease (33.0 +/- 9.1 percent, mean +/- standard deviation) in the myocardial uptake of rubidium-82 was detected only when flow was increased by more than 120 percent in relation to a control area after administration of dypiridamole. The technique using rubidum-82 and tomography was applied in five volunteers and five patients with angina pectoris and coronary artery disease. Myocardial tomograms recorded at rest and after exercise in the volunteers showed homogeneous uptake of cation in reproducible and repeatable scans. In contrast, the patients with coronary artery disease showed an absolute mean decrease of 36 +/- 14 percent in regional myocardial uptake of rubidium-82 after exercise. These abnormalities persisted in serial tomograms for more than 20 minutes after the symptoms and electrocardiographic signs of ischemia.