Four cases of pulmonary artery stenosis resulting from extrinsic pressure are presented. All of these cases presented with the triad of chest pain, dyspnoea, and a pulmonary systolic murmur. Respiratory variation of this murmur was noted in three of the patients, the murmur increasing during expiration and diminishing or disappearing during inspiration. It is suggested that this may be a useful sign in diagnosing this syndrome. The tumour in these four cases was an intrapericardial sarcoma, a benign teratoma, Hodgkin's disease, and a malignant thymoma respectively.