It is possible that Des-Arg9-bradykinin, the active metabolite of bradykinin and selective bradykinin B1 receptor agonist contributes to the regulation of cardiovascular functions, but little is known about the role of this peptide on coronary vascular tone and heart rate. Furthermore, the possible action of Des-Arg9-bradykinin on contractile force, +dP/dtmax and -dP/dtmin has not been investigated. Therefore, I studied the probable effects of the peptide on coronary perfusion pressure, heart rate, left ventricular developed pressure (the index of cardiac contractility), +dP/dtmax (the maximal rate of pressure development) and the -dP/dtmin (the maximal rate of pressure fall) in rat hearts. The hearts were isolated under light ether anesthesia and perfused under constant flow conditions (12 ml/min) with modified Krebs-Hanseleit solution and 10, 100 and 1000 nM Des-Arg9-bradykinin infused to the hearts for 30 min. Ten and 100 nM Des-Arg9-bradykinin did not change the heart rate but, 1000 nM increased significantly (p<0.01). All the doses of Des-Arg9-bradykinin caused a significant reduction in perfusion pressure, developed pressure, +dP/dtmax and -dP/dtmin (p<0.001 for all). There is sufficient evidence from this study that Des-Arg9-bradykinin possesses vasodilatory efficacy with a modest negative inotropic action. These results might suggest that Des-Arg9-bradykinin can also decrease contraction and relaxation rate. Furthermore, higher dose of the peptide may exert tachycardic action.