Fifteen patients with moderately severe and severe chronic congestive heart failure were studied to determine the central haemodynamic results of short term increases in lower body positive pressure. Central haemodynamic variables were determined by Swan-Ganz thermodilution catheterisation and arterial cannulation. Graded increases in lower body positive pressure were applied to supine patients using Medical Anti-Shock Trousers (MAST). Increasing lower body positive pressure by 25 mm Hg and 55 mm Hg caused increases in mean right atrial pressure (6.0 to 13.2 to 17.9 mm Hg; p less than 0.001 and p less than 0.0001 respectively) and mean pulmonary artery pressure (26.8 to 35.5 to 41.3 mm Hg; p less than 0.05 and p less than 0.01 respectively). No significant changes were seen in left heart filling pressures or in pulmonary vascular resistance. Furthermore, there were no significant increases in indices of cardiac work (cardiac index, left ventricular stroke work index, right ventricular stroke work index or cardiac power output) despite the increased right heart filling pressures. These results show that in patients with longstanding severe congestive heart failure, short term increases in cardiac return may increase right heart pressures but do not appear to cause either beneficial or detrimental changes in left heart haemodynamic indices.