A patient who had myelodysplastic syndrome (MDS) and dilated cardiomyopathy (DCM) had a transient improvement of cardiac function after peripheral blood stem cell transplantation (PBSCT). When he was admitted to hospital for PBSCT, a chest X ray showed cardiomegaly, and Tc-99m quantitative gated single photon emission computed tomography (QGS) showed increases in left ventricular (LV) volumes and a decrease in LV ejection fraction (LVEF). A coronary angiogram showed no evidence of coronary artery disease. Left ventriculography showed similar findings as QGS, and the findings from a myocardial biopsy were compatible with DCM. Three months after a successful allo-PBSCT with his brother as the donor, the cardiomegaly had been attenuated, the LV volumes decreased and LVEF increased on the QGS images. However, 10 months later, his cardiac function had deteriorated. The changes in cardiac function did not correlate with the hematological changes, such as the hemoglobin level.