Amrinone, an inotrope with vasodilating properties, is of potential use in managing the right ventricular failure and pulmonary vasoconstriction induced by massive pulmonary embolism (PE). Therefore, to determine the hemodynamic effects of amrinone in a canine model of massive PE, autologous blood clot was infused into ten dogs (eight treated and two control animals) in an amount sufficient to decrease mean systemic arterial pressure (MAP) by at least 25 percent. This resulted in an increase in mean pulmonary artery pressure (MPAP) from 13.4 +/- 3.7 mm Hg to 44.4 +/- 4.8 mm Hg (p less than 0.01), a decrease in MAP from 122 +/- 9.5 mm Hg to 35.6 +/- 9.8 mm Hg (p less than 0.01), and a decrease in cardiac output from 2.73 +/- 0.834 L/min to 1.22 +/- 0.61 L/min (p less than 0.01). Amrinone was administered in an initial bolus of 0.75 mg/kg followed by an infusion of 7.5 micrograms/kg/min, which resulted in significant hemodynamic improvement in all subjects, with a fall in MPAP to 35.3 +/- 5.1 mm Hg (p less than 0.01), an increase in MAP to 98.1 +/- 31.1 mm Hg (p less than 0.01), and an increase in cardiac output to 2.01 +/- 0.7 L/min (not significant) at 5 min. Cardiac output continued to increase to 2.56 +/- 0.16 L/min (p less than 0.01) at 35 min. We conclude that amrinone alleviated pulmonary hypertension, systemic hypotension, and low cardiac output in a canine model of massive PE.