The biochemical and biophysical properties of the normal and failing human heart differ. Tension development of skinned myocardium from the failing heart has been found to be more sensitive to calcium than that from the normal heart, while maximal myofibrillar ATPase activity is depressed in the failing heart. Renal hypertension was induced in rats by employing 2-kidney-1-clip model (2K1C). Blood pressure was recorded by introducing a catheter through the left carotid artery. A Statham p23 DC transducer was used and the pressure was recorded on a Grass Polygraph. The heart was mounted and Action potential recording from papillary muscle. Myocytes were isolated from rat according to the method of Mitra and Morad (1981). The contraction of the heart were recorded for 90 min. The starting amplitude of contraction was calculated as 100% a drop in the amplitude of contraction over the 60 min was observed to be 80%. This drop in amplitude of contraction was not significant. The observations indicate that the APD 40 is most sensititve to calcium alteration in the superfused buffer. The rat myocytes were studied by flow-cytometr.