An aneurysm of a saphenous vein graft (SVG) is a rare but potentially fatal complication of coronary artery bypass grafting (CABG). We describe a case of a large SVG aneurysm (7 x 6 cm) compressing the right atrium. The patient presented with chest pain, dyspnea and desaturation, and a right intra-atrial mass was revealed on echocardiography. The differential diagnosis of intracardiac masses revealed by echocardiography should include extrinsic lesions. Due to its potential lethal complications, an SVG aneurysm should be considered in a post-CABG patient presenting with acute coronary syndrome or heart failure.