The effect of Danshen (Radix salviae miltiorrhizae) on mechanical activity and coronary flow rate of isolated rat hearts was examined to assess the ability of Danshen to protect the myocardium against the effects of ischemia and reperfusion. After 20 min of control perfusion, in the presence or absence of Danshen, the hearts were made totally ischemic for 30 min and then reperfused for 30 min. Danshen had a negative inotropic effect and caused an increase of coronary flow rate. During post-ischemic reperfusion recovery of left ventricular developed pressure in the Danshen-treated hearts was significantly better and contracture was significantly less than in the untreated hearts. The results indicate that Danshen protects the heart against some of the deleterious effects of ischemia and reperfusion.