A 29-year-old man with pectus excavatum presented with exercise intolerance, pulsus paradoxus, and paradoxically split S2. Chest computed tomography (CT) showed the heart shifted leftward and a pectus severity index of 7.18. Cardiopulmonary exercise study showed reduced VO2max, anaerobic threshold, and oxygen pulse. Echocardiography revealed a decline in mitral and tricuspid valve inflow, and stroke volume during inspiration. Cardiac extrinsic compression and anatomic cardiac abnormalities were not present. Dynamic magnetic resonance imaging (MRI) demonstrated inspiratory inferior vena cava (IVC) compression at the diaphragm. We discuss IVC compression by the diaphragm as a source of patient symptoms and as a mechanism for pulsus paradoxus associated with pectus excavatum.