Simultaneous recordings of airway pressure, pleural pressure, and right ventricular (RV) pressure were obtained during mechanically controlled ventilation in a group of patients requiring respiratory support. Changes in transpulmonary pressure (calculated as airway pressure minus pleural pressure) were measured at end-expiration and end-inspiration during intermittent positive pressure ventilation with or without the application of a positive end-expiratory pressure, and were related to RV isovolumetric pressure changes at the onset of systole. It was found that any increase in transpulmonary pressure by intermittent positive pressure ventilation, or positive end-expiratory pressure (PEEP), or both, was associated with a proportional increase in RV isovolumetric pressure change. Moreover, when lung volume was progressively increased by incremental increases in tidal volume or PEEP level, transpulmonary pressure and RV isovolumetric pressure changes were strongly and linearly correlated. These results suggest that: 1) RV isovolumetric pressure change might be used as an index of RV output impedance during respiratory support by mechanically controlled ventilation; and 2) lung inflation resulting from the use of a positive airway pressure during respiratory support can increase RV output impedance and thereby contribute to the decrease in RV stroke output.