In 44 patients undergoing operation for mitral disease, the pulmonary volumes, the pulmonary mechanics and the alveolocapillary transfer of CO were examined prior to the operation and 3 times postoperatively: in the 3rd or 4th wk, between the 3rd and 5th mth and between the 10th and 14th mth. During the immediate postoperative period an episode of considerable aggravation of functional impairment was observed which was not due exclusively to the surgical trauma of the chest wall but also to specific affection of the alveolocapillary membrane. One year postoperatively, the preoperative functional alterations were found to have only partially returned. In particular, the transfer of CO and the resistance of the respiratory tract remained abnormal even in cases running a favorable clinical course. The possible causes of these phenomena are discussed. (11 references).SCOPUS: NotDefined.jinfo:eu-repo/semantics/publishe