The use of nitroglycerin as a vasodilator in the treatment of congestive heart failure has demonstrated that the hemodynamic response is related to the degree of left ventricular dysfunction. Little emphasis has been placed on the mechanisms responsible for the variability in heart rate response to nitroglycerin. To study this problem, 33 patients with a variety of chronic cardiac disorders were given 0.4 mg of nitroglycerin sublingually. An increase in heart rate of less than 3 beats/min to sublingual nitroglycerin allowed a clear identification of a group of patients who had a left ventricular end-diastolic pressure greater than 18 mmHg or pulmonary artery mean pressure greater than 22 mmHg, and who had improvement in hemodynamic parameters following nitroglycerin. This alteration in baroreceptor sensitivity appears to be related to the level of left ventricular filling pressure, and can be used as a simple bedside means of identifying a group of patients who benefit the most from the vasodilator action of nitroglycerin.