p ULMONARY compliance has been shown to be decreased for a period of several weeks following anesthesia and open-heart operations." 2 This postoperative decrease in compliance is a further change from the low preoperative values seen in patients with heart disease and pulmonary hypertension.34 The prolonged postoperative decrease in pulmonary compliance has not been correlated with changes in lung volumes or in pulmonary gas exchange. The purpose of this study is to relate changes in compliance to other pulmonary functions in the postcardiotomy patient an an attempt to simplify the study of pulmonary function in patients who undergo operations on the heart. METHODSPatients with mitral stenosis were studied before and after cardiac bypass. The subjects were studied in the supine position on four occasions: preoperatively, I to 2 days prior to operation; in the recovery room immediately after operation while breathing continued spon-*Presented at a meeting