Right ventricular function was investigated in seven asthmatic patients during an acute attack, using simultaneous bedside right heart catheterization and two-dimensional echocardiography (2DE). Hemodynamic and echocardiographic data were compared during four successive periods of the respiratory cycle: inspiration, early expiration, mid-expiration, and late expiration. During inspiration, 2DE showed a significant increase in right ventricular area at both end-systole and end-diastole. This inspiratory right ventricular enlargement coexisted with a significant reduction in 2DE stroke area and pulmonary artery pulse pressure suggesting an inspiratory reduction in right ventricular stroke output. A transient depression of right ventricular function during deep inspiratory effort in asthma was thus strongly suggested. The negative pressure surrounding the right ventricle at inspiration is advocated as the causative factor enabling reduction in the hydraulic force effecting right ventricular ejection. The highly negative pleural pressure probably holds the right ventricular free wall and restrains its systolic inward motion, as suggested by the finding of a concomitant inspiratory reduction in right ventricular developed pressure and 2DE fractional area contraction.