PURPOSE: The study was designed to investigate the effect of cis-dichlorodiammineplatinum(II)(cis-DDP) on the radiation-induced cardiomyopathy in the rat. MATERIALS AND METHODS: The myocardial damage was assessed by histopathologic changes. In radiation alone group, radiation dose ranged from 10-40 Gy X-ray in a single dose and in combined group, cis-dichlorodiammineplatinum(II) at a dose of 6mg/kg was given intraperitoneally immediately after irradiation of same dose with X-ray alone group. RESULTS: The early changes by radiation included congestion, inflammatory cell infiltrations and fibrosis in myocardial interstitium with focal myocardial necrosis, which was noted in 10 Gy group. Myocardial fibrosis was increased by increasing dose of radiation but myocardial necrosis was not proportional to radiation dose. cis-DDP along group showed minimal degeneration of myocardium with surrounded by imflammatory cell infiltration. In combined group, myocardial fibrosis in 10 Gy group were similar to radiation along group, but 30 Gy and 40 Gy groups showed serverer changes. Electron microscopic examination showed disruption of Z-band and edema of mitochondria with decreased matrix density in 20 Gy radiation group which were serverer in 40 Gy radiation group. Combined group showed endothelial changes and disruption of Z-band worse than radiation alone group as well as increased connective tissue, which was considered as a hallmark of late change in radiation-induced heart disease. CONCLUSION: This results showed minimal enhancement of the radiation-induced cardiomyopathy in rats by cis-DDP.