1. The limited therapeutic role of pulmonary vasodilation reflects lack of their selectivity for the pulmonary vasculature, and many drugs have been evaluated for effectiveness; however, none has gained widespread clinical use. 2. Milrinone (MIL) is a newly synthetized phosphodiesterase inhibitor, which has potent positive inotropic and vasodilatory effects. 3. The present study shows the effects of MIL on the pulmonary circulation in dogs with pulmonary hypertension due to autologous muscle-induced pulmonary embolism, and also demonstrates a comparison with those of dopamine and dobutamine. 4. As MIL showed potent vasodilatory effects on the pulmonary vasculature, it had a potential clinical role in the treatment of pulmonary hypertension.