The pulmonary vasodilator effect of ZSY-27, a newly synthesized phosphodiesterase inhibitor, was studied in dogs with pulmonary hypertension resulting from autologous muscle-induced pulmonary embolism (PE). A bolus injection of ZSY-27 (1 mg/kg) significantly decreased mean pulmonary arterial pressure from 32 +/- 4 to 24 +/- 5 mm Hg and pulmonary vascular resistance index from 415 +/- 60 to 316 +/- 94 dyne.sec/cm5.m2. ZSY-27 did not change mean arterial pressure. The cardiac index was slightly increased and the systemic vascular resistance index was slightly decreased after ZSY-27 injection, but these changes were not statistically significant. This study suggests that ZSY-27 is a possible therapeutic agent for pulmonary hypertension secondary to PE.