Radioimmunoassays were used to measure the concentration changes of plasma endothelin（ET） and atrial natriuretic peptide（ANP） during the onset and after termination of paroxysmal supraventricular tachycardia（SVT）. 30 cases were reviewed and compansons with 42 normal subjects were made. There are very significant differences（P<0.0001） in the concentration changes of both plasma ET and ANP during the onset and 30 minutes after the termination of SVT. During the onset period of SVT. the plasma ET and ANP were markedly elevated and 30 minutes after its termination they were lowered significantly

but their concentrations were still 2-fold higher than ihose of the control group. As the biological effects of ANP and ET are antagonistic to each other. their parallel elevation and lowering of plasma concentrations during and.after the termination of SVT reveal that these 2 hormones parucipate in the pathophysiological process of SVT. This phenomenon is possibly one of the homeostatic regulatory functions in the organism.