Doxorubicin (DXR), administered iv in rats at the weekly dose of 3 mg/kg for 5 weeks, significantly impaired body weight gain and induced irreversible ECG alterations, mainly consisting of a progressive prolongation of ST and QT intervals. Five weeks after the last DXR administration, the contractile performance of atria isolated from treated animals was significantly reduced. At the same time, relevant morphologic lesions, consisting of myocyte vacuolization and myofibrillar loss, were also present in the myocardium of the same rats. The study showed that ICRF-187, administered ip at a dose of 125 mg/kg, significantly prevented body weight loss. QT and ST prolongation, and the decreased contractile force induced by DXR. In addition, ICRF-187 caused a significant reduction in incidence and severity of myocardial lesions. The cardioprotective effect of ICRF-187 is not mediated by a modification in DXR pharmacokinetics in heart, since the drug was actually found to increase DXR uptake in myocardial cells.