OBJECTIVE To compare the hemodynamic effects of medical antishock trousers (MAST) inflation in mechanically ventilated patients with normal and poor left ventricular function. METHODS Twelve patients requiring respiratory support were divided into two groups according to baseline transesophageal echocardiography (TEE) measurements: normal left ventricular dimensions and fractional area of contraction (FAC=61 +/- 5%) (n=7) and dilated cardiomyopathy with reduced FAC (21 +/- 1%) (n=5). All patients were studied when two successive levels of load (mild load by inflation of the leg compartment of MAST at 50 cmH2O and high load by adding the abdominal compartment of MAST inflated at 30 cmH2O) were applied. Global left ventricular systolic function was assessed on the TEE transgastric short-axis view. End-systolic wall stress (ESWS) was used as an indicator of left ventricular afterload. RESULTS Total respiratory, lung and chest wall compliances were reduced by 48%, 51% and 27% respectively at the high load level (P < 0.05). Whereas no hemodynamic changes occurred at mild load, the high load level produced an increase in left ventricular afterload as evidenced by concomitant increases in diastolic arterial blood pressure (66 +/- 6 to 79 +/- 6 mmHg, P < 0.05) and ESWS (69 +/- 12 to 74 +/- 12 Kdyn x cm(-2) x m(-2), P < 0.05). In patients with dilated cardiomyopathy, this increase in afterload impaired the left ventricular systolic function and end-systolic area increased (19.0 +/- 2.5 to 21.4 +/- 2.9 cm2 x m(-2), P < 0.05) while FAC decreased (22 +/- 2 to 16 +/- 2%, P < 0.05). Left ventricular end-diastolic area remained unchanged during the study in both groups. CONCLUSIONS MAST inflation impairs respiratory mechanics and global left ventricular systolic function in cardiac patients without changes in left ventricular preload.