The purpose of this study was to investigate the influences of vesnarinone, newly synthesized in the School of Pharmacy, West China University of Medical Sciences in 1985, on the circulatory and respiratory functions of dogs. Eight dogs were anesthetized with 3% sodium pentobarbital. Vesnarinone (2 mg/kg), dimethyl sulphoxide (the solvent which was needed to prepare solution of OPC-8212), and 0.9% NaCl (normal control) was given separately according to the arrangement of Latin square. The ECG, blood flow, blood pressure and respiration were measured and recorded for 1-15 minutes. Vesnarinone increased the blood flow in the common carotid artery with no significant changes in blood pressure, heart rate, or respiration. These results suggest that OPC-8212 has positive inotropic effect but no effect on the heart rate in anesthetized dogs.