The authors produced an acute canine heart failure model by injecting microspheres (ø15.5 ±0.1 mm, 5 X 105) into the left coronary artery, and characterized the model in terms of the pressure-volume relationship obtained by the conductance catheter method. Cardiodynamics of the microsphere injection group (M group: n=10) and control group (C group: n=12) were studied with 1) heart rate, 2) aortic pressure, 3) cardiac output (CO), 4) maximal ventricular elastance, 5) effective arterial elastance/maximal ventricular elastance, and 6) external work/pressure-volume area efficiency. With microsphere injection, CO and external work/pressure-volume area efficiency significantly decreased. With administration of dobutamine (5 mg/kg/ min), CO and maximal ventricular elastance recovered to normal and aortic pressure became higher than normal. These changes in heart rate, aortic pressure, CO, maximal ventricular elastance, and external work/pressure-volume area efficiency in the M group were comparable in percentage to those in the C groups. Cardiodynamics of this heart failure model generally were stable for 3 hrs after microsphere injection. The authors concluded that this model would be an excellent acute heart failure model for investigating hemodynamic effects of circulatory assist devices.