4'-epidoxorubicin (4'-epiDXR) was compared with doxorubicin (DXR) for myocardial effects in rabbits. Histologically, both drugs when given for six weeks induced a high incidence of diffused myocardial damage. The myocardial damage was less evident in rabbits treated with 4'-epiDXR than DXR for 3 weeks. Functionally 4'-epiDXR like DXR significantly reduced cardiac index (CI), stroke index (SI) and mean arterial blood pressure (MAP).