The aim of the present study was to determine whether induction of ischaemic heart failure by micro-embolization leads to only a single episode of myocardial injury or whether it sets up a vicious cycle of progressive myocardial damage. Acute left ventricular (LV) failure was produced in 15 closed-chest anaesthetized dogs by injection of 50 microns plastic microspheres into the left main coronary artery. The dogs showed signs of severely depressed LV function; there was a marked increase in LV end-diastolic pressure and a marked decrease in stroke volume. Myocardial lactate uptake decreased or reversed to production. Six dogs with very high LV end-diastolic pressure died during the subsequent 3 days and autopsy revealed pulmonary edema. The LV function was re-examined in four dogs at 2 and 4 weeks after embolization. Except for a modest elevation of LV end-diastolic pressure there were no haemodynamic or metabolic signs of myocardial dysfunction. Gross and light microscopic examination of the heart in dogs 8 hours to 6 weeks following microsphere injections revealed numerous small infarcts or focal areas of granulation or scar tissue throughout the entire left ventricle. At 1 to 6 weeks close to the infarcts there were scattered myocytes with strong eosinophilia and pyknosis or loss of nuclei, interpreted as myocytolysis. In two dogs killed at six weeks after the embolization there were areas of granulation tissue, similar to a recent infarction about 1 week old. Thus, in spite of apparent functional restoration there were morphological signs of repeated and progressive myocardial injury several weeks after coronary embolization.