To study the effects of batroxobin on coronary circulation and cardiac performance in acute myocardial ischemia, Batroxobin was given intravenously to dogs with experimental coronary stenosis. A dose-dependent increase of coronary blood flow (CBF) was observed. Forty minutes after batroxobin (2 BU.kg-1 at infusion rate 0.1 BU.kg-1.min-1) administration, CBF increased by 12% (P < 0.05), small coronary resistance(RS) decreased from 4.1 +/- 0.5 to 3.2 +/- 0.5 mmHg.min.ml-1 (P < 0.01), while large coronary resistance(RL) changed insignificantly from 3.9 +/- 0.8 to 3.8 +/- 0.7 mmHg.min.ml-1 (P > 0.05). Two hours following drug administration, the changes in CBF, RS and RL still remained and RT decreased by 13% (P < 0.05). The + LV(dp/dt)max and -LV(dp/dt)max increased by 14% and 16% (P < 0.05) respectively compared with those in control group. It is concluded that batroxobin improves the ischemic canine coronary circulation and cardiac performance by way of lowering the small coronary resistance and thus increasing CBF. The data also suggest the benificial effect of batroxobin in acute myocardial ischemia.