We studied the acute hemodynamic effects of increasing nasal continuous positive airway pressure (CPAP) in 13 patients with acute decompensation of congestive heart failure. Heart rate, respiratory rate, pulmonary capillary wedge pressure, right atrial pressure, systemic blood pressure, and thermodilution cardiac outputs were measured at baseline, during, and after application of nasal CPAP at increasing pressures of 5, 10, and 15 cm H2O. Cardiac index, stroke volume, and oxygen delivery were calculated. Based on a significant change in cardiac output greater than or equal to 400 ml, seven patients were classified as responders, whereas six patients were considered to be nonresponders. In responders, significant increases were noted in cardiac index (2.5 +/- 0.7 to 2.9 +/- 0.9 L/min/m2), stroke volume (49 +/- 15 to 57 +/- 16 ml), and oxygen delivery (10.3 +/- 5.1 to 12.3 +/- 6.0 ml/min/kg) without a change in pulmonary capillary wedge pressure. In contrast, the nonresponders showed no significant change in any of the hemodynamic parameters. Improvement in cardiac output could not be predicted by any of the baseline hemodynamic or clinical variables, nor was it related to random variations since all variables returned to baseline after cessation of CPAP. Increase in stroke volume without a change in pulmonary capillary wedge pressure (preload) suggests either improved inotropic function of the left ventricle or reduced left ventricular afterload with CPAP. Thus, CPAP may offer a new noninvasive adjunct to improving left ventricular function and augmenting cardiac performance in a subset of patients with congestive heart failure.