A 55-year-old man, with a history of nephrectomy for renal cell carcinoma, was evaluated using radionuclide angiocardiography to exclude cardiac shunts as the cause of vascular bruits heard at auscultation. A pulmonary time-activity curve derived from the right lung showed a pattern typical of a large left-to-right shunt, whereas that from the left lung was normal. Increased systemic arterial flow to the lateral right chest was noted in early dynamic images. Subsequent studies revealed that this flow and the abnormal time-activity curve of the right lung were due to systemic arterial supply to metastatic pleural cancer, originating from the kidney. The authors conclude that special caution should be undertaken in the interpretation of the radionuclide angiocardiography for determining left-to-right cardiac shunts, especially in those showing a asymmetric pulmonary time-activity curve.