The postpericardiotomy syndrome is a febrile illness with pericardial and pleural reaction that either persists or appears beyond the 1st postoperative week. We believe that it begins in the 1st week after intrapericardial cardiac surgery, and that clinical signs of illness correlate with appearance of AHA and with significant rise in titer to AVA. Our present working hypothesis is that myocardial damage with bleeding into the pericardial sac at the time of surgery combines with concurrently acquired or reactivated viral illness to set the stage for the syndrome. The immune response is triggered by viral invasion of traumatized myocardium and an immune response is mounted, not against autologous myocardium per se but against the neo-antigen, the virus-infected myocardium. The illness is self-limited. It sometimes recurs but it seems to leave no sequelae other than the bad memory of a painful postoperative complication that prolonged hospitalization and delayed the realization of the full benefits of that heart operation.