The occurrence of constrictive pericarditis after coronary bypass surgery is rare and clinical manifestations may appear at variable intervals after surgery. Three possible causes have been postulated, all of which were probably involved in the case which we describe. The clinical diagnosis of postoperative constriction is difficult and not often considered. It is best confirmed by means of cardiac catheterization, which shows typical haemodynamic features. Surgical treatment is both difficult and a threat to the coronary bypass grafts, when present. Conservative management with diuretics is preferred unless constriction is severe.