Aim The changes of the membrane fluidity (MF) and Ca2+-ATPase activity of the cardiac sarcoplasmic reticulum(SR) and relation between them were investigated in venovascular hypertensive rats and normotensive rats.Methods Two-kidney, one-clip(2klc)renovascular hypertension was produced in SD rats by constriction of the left renal artery with a silver clip. Thirty-two rats were randomly divided into four group : animals made hypertensive for 6 weeks( H6 ) and 10 weeks (H10) , respectively. And age-matched control rats ( C6 and C10) underwent sham surgery.The membrane enriched with SR was isolated by a modified of Harigayas and Schwartz' s method.The cardiac SR Ca2+-ATPase activity and SR MF were determinated by James' and fluorescent polarization methods,respectively. All values are x±sand were analyzed with an analysis of variance and a student's test.Results The cardiac SR Ca2+-ATPase activity and MF in hypertensive rats seemed like a tendency to reduce to compared with those in normotensive groups.But it was no statistical difference between them. With age growing, the MF of cardiac SR in all rats showed a decline tendency, especially, in hyperteinsive groups(H10 vs H6,P<0. 05).Conclusions The above results suggest that the change of Ca2+-ATPase activity was as a same tendency as one of MF in the cardiac sR of hypertensive groups. The SR Ca2+-transport function was no reduced significantly during 6 or 10 weeks when the hypertension continued, one of the reasons that cardiac SR MY dropped markedly during short period might be an influence of hypertension.