Abstract: The effects of DHAP on electrical and mechanical activities were investigated by synchronously recording action potential and isometric tension in isolated myocardium. No influence was demonstrated on action potential (APA, APD₂₀、APD₉₀) by DHAP 10^-5～10^-3M in guinea pig palillary muscle. The inhibition on the force of contraction with the same concentration of DHAP, however, was shown in a concentration-dependent way. The effects of DHAP on the electrical and mechanical activities in cat papillary muscle were similar to those in guinea pig papillary muscle. With the dose of DHAP 10^-5～5×10^-4M, alteration of action potential of pacemaker cells was not observed in the isolated sinus node preparation of the rabbit. When the dosage was increased to 10^-3 M, the electrical activities were inhibited. The experimental results indicate that the effects of a certain dose of DHAP on inhibiting the tension in myocardium are available in clinical application. A warning is given that an increase in dosage may enhance the inhibition on contractile force in myocardium and inhibit the automaticity of sinus node pacemaker cells.