Perfusion with human serum albumin decreased myocardial hydrogen peroxide (H2O2) levels (as assessed by inactivation of myocardial catalase activities following aminotriazole pretreatment) and increased myocardial ventricular developed pressures (DP), contractility (+dP/dt) but not relaxation rate (-dP/dt) in isolated crystalloid perfused rat hearts subjected to normothermic global ischemia (20 min) and then reperfusion (40 min). Albumin also decreased H2O2 concentrations in vitro. The findings support the possibility that albumin may act as a protective O2 metabolite scavenger in vivo.