The effects of amrinone on cardiac contraction and relaxation were assessed in isolated, perfused rat hearts. It was found that the left ventricular developed pressure (LVDP). dp/dtmax and -da/dtmax did not significaptly increase, and the time constant (τ) did not markedly shorten with perfusion of low concentration (1 nmol/L. 100 nmol/L) of amrinone. The perfusion with higher concentration (1000 nmol/L) of amrinone. reduced LVDP (P<0.01), dp/dtmax (P<0.01), -dp/dtmax, (P<0.01), and prolonged τ (P< 0. 05) significantly. It was assumed that amrinone has no direct positive inotropic effect, and can not improve cardiac relaxation. On the contrary, the cardiac contraction and relaxation will be inhibited at higher concentration of amrinone.