Acute left ventricular failure was induced in anaesthetized dogs by repeated embolization of the left coronary artery with 57 micron microspheres. Tissue blood flow was measured with isotope-labelled microspheres in two stages of heart failure. With increasing doses of embolizing solution there was a progressive decline in systemic blood pressure and cardiac output. Failure was accompanied by a significant decrease in blood flow in all tissues examined except for intestine, adrenal gland, skin and right ventricle. Overall cardiac output distribution was estimated by combining flow data with data on relative tissue weights obtained from a dissection study in a separate group of dogs. A selective redistribution of cardiac output took place in the failure state. The blood flow was redirected away from the skeletal muscles and the spleen in favour of the intestines, kidneys, heart and brain.