We compared the time-course of the hemodynamic effect of isosorbide dinitrate (ISDN), 5 mg, in the form of sublingual tablet and oral spray, in 15 patients with isolated chronic pulmonary congestion (pulmonary arterial end-diastolic pressure of 15 mmHg or more in the presence of normal or only slightly reduced cardiac index). Both formulations produced significant reductions in the pulmonary arterial end-diastolic pressure. The effect of ISDN tablet (sublingually) became evident at 10 minutes after administration and was maximal at 30 minutes. The effect of ISDN oral spray became evident at 3 minutes and reached a peak at 10 minutes. The magnitude of hemodynamic response was similar. These findings indicate that ISDN oral spray is superior to ISDN sublingual tablets for rapid relief of pulmonary congestion.