Transient pulsus alternans was induced by isosorbide dinitrate (ISDN) in a patient with postmyocarditis congestive heart failure under diuretic therapy. The severity and duration of pulsus alternans depended on the dose of ISDN. According to the echocardiographic and hemodynamic examinations, the superimposed preload reduction caused by ISDN combined with decreased blood volume owing to diuretic therapy most likely contributed to the development of pulsus alternans.