Abstract: Tetrandrine (Tet) 10 mg/kg or verapamil (Ver) 0.4 mg/kg iv decreased cardiac contractility as shown by the lowering of dz/dt max, prolongation of Q-Z interval and decrease of Heather index in anethetized dogs. The pump function parameters of the heart-CO, CI, SV,SI and TTI were reduced concomitantly. Since both drugs decreased HR, TPR and TTI, the oxygen consumption of the heart might be reduced accordingly.The fact that the effects of Tet and Ver on the heart performance are very similar and can all be reversed by calcium chloride gives further support to the speculation that Tet might be a slow channel blocker.