An assessment of the acute hemodynamic effect of intravenous isosorbide dinitrate (ISDN) was performed with a Mikro-tip angiocatheter in 10 patients during the diagnostic cardiac catheterization. Both left ventricular (LV) systolic pressure (SP) and end-diastolic pressure (EDP) were decreased by 2 mg of ISDN. Cardiac index, stroke work index and heart rate did not change significantly, and neither systemic vascular resistance nor pulmonary arteriolar resistance was reduced. Isovolumic phase and ejection phase indices of contractility were not altered. End-diastolic stress, an accurate index of preload, was reduced significantly (47.0 +/- 27.6 to 28.7 +/- 24.6 g/cm2, p less than 0.01), and mid-systolic stress, an index of afterload, was also reduced (371 +/- 102 to 332 +/- 85 g/cm2, p less than 0.05). No undesirable side effects were noted during this study. We concluded that bolus intravenous (IV) ISDN safely reduced both preload and afterload. As 2 mg of IV ISDN had no significant change on SVR, a larger dose of ISDN bolus injection might be needed for a significant arterial vasodilating effect. Bolus IV ISDN seems to be very effective in cases in which rapid reduction of LV filling pressure is mandatory.