Comprehensive cardiopulmonary and metabolic monitoring of severely traumatized patients for 7 days from the time of injury has allowed us to determine parematers which correlate with survival and nonsurvival. The earliest and most persistent change is an increased pulmonary vascular resistance which results in right heart overload and failure. Left heart "failure" which has been previously described with acute respiratory failure and shock is shown to be a mathematical artifact caused by dilatation of the right heart and encroachment on left ventricular filling volume. Causes of death in most patients were not directly referable to right heart dysfunction but we postulate that hypercoagulability and microembolism could independently produce the observed pulmonary vascular changes as well as the multiple organ failure which usually was responsible for death. Resolution of this question will require more sophisticated hematologic evaluation.