Chest physiotherapy (CPT) is used frequently in the ICU, but there is little available information that quantitates its effect on cardiac or respiratory function. Nineteen mechanically ventilated patients with post-traumatic respiratory failure were studied before, immediately after, and 2 h after CPT was used to manage secretion retention. Cardiac index was unchanged, but there was an immediate decrease in intrapulmonary shunt, followed 2 h later by an increase in lung/thorax compliance. We did not find the reduced cardiac output reported by others. The reasons for this may include use of different CPT techniques, a young patient population (mean age 32.4 yr), and mechanical ventilation with positive end-expiratory pressure. CPT did not produce the deleterious cardiopulmonary changes associated with bronchoscopy, and it reduced retained lung secretions without producing hypoxemia. Intrapulmonary shunt and lung/thorax compliance were significantly improved, but the long-term clinical effect of these changes is unknown.