Objective To detect changes in the calcium pump protein or the calcium release channel of thesarcoplasmic reticulum during chronic doxorubicin treatment. Methods The rats were treated with intravenousdoxorubicin(lmg/kg) twice weekly for 12 to 18 times. Controls received intravenous normal saline. The seventy ofcardiomyopathy was scored by light and electron microscopic study to investigate left ventricular papillary muscleand the calcium handling of the myocardial sarcoplasmic reticulum (SR) was determined using the isotope45 Ca2+loading. Results The ability of SR Ca2+ uptake was decreased in doxorubicin- treated rats compared withcontrol rats and the magnitude of the decrease in SR Ca2+ uptake was correlated with the seventy of thecardiomyopathy graded by pathology score. The percentage of the SR calcium release decreased 14.3% ± 4.2% in theinitial 10s and decreased 17.1 %± 4.5% (P<0.05) at 2min in the severe groups as compared with control (P<0.01)and the amount of SR calcium release seemed correlate with the seventy of the cardiomyopathy graded.Conclusion The altered function of SR calcium uptake and release could lead to the abnormalities of contractionand relaxation observed in the doxorubicin cardiomyopathy. Objective To detect changes in the calcium pump protein or the calcium release channel of the sarcoplasmic reticulum during chronic doxorubicin treatment. Methods The rats were treated with intravenous dooxorubicin (lmg / kg) twice weekly for 12 to 18 times. Controls received intravenous normal saline. The seventy ofcardiomyopathy was scored by light and electron microscopic study to investigate left ventricular papillary muscle and the calcium handling of the myocardial sarcoplasmic reticulum (SR) was determined using the isotope 45 Ca2 + loading. Results The ability of SR Ca2 + uptake was decreased in doxorubicin-treated rats withcontrol rats and the magnitude of the decrease in SR Ca2 + uptake was correlated with the seventy of the cardiomyopathy graded by pathology score. The percentage of the SR calcium release decreased 14.3% ± 4.2% in theinitial 10s and decreased 17.1% ± 4.5% (P < 0.05) at 2 min in the severe groups as compared with control (P <0.01) and the amount of SR calcium relea se deemed correlate with the seventy of the cardiomyopathy graded. Confluenced The altered function of SR calcium uptake and release could lead to the abnormalities of contraction and relaxation observed in the doxorubicin cardiomyopathy.