A 41-year-old man with a partially cystic cardiac mass was referred to our institutions. About 17 years previously, he had undergone the excision of a lipoma in the left popliteal region. The patient had been well until 3 to 4 months earlier, when dyspnea on exertion developed. Two-dimensional echocardiography (Figure 1A and 1B), computed tomography (Figure 2A and 2B), and magnetic resonance imaging (Figure 3A and 3B and Movies I–3 in the online-only Data Supplement) displayed a patchy lobulated epicardial mass (transversal diameter, 7 cm; thickness, 4 cm) near the left cardiophrenic angle, partially occupying the left ventricular chamber. Figure 1. Echocardiography. Apical 4-chamber view showing a large cardiac mass infiltrating the apex, lateral, and anterior walls of the left ventricle. A second small cardiac mass is attached to the left wall; presence of pericardial effusion. Contrast-enhanced ultrasound shows the large infiltrative cardiac mass. Inside the mass are large nodular, nonperfused or hypoperfused areas surrounded by vascularized nonmyocardial tissue infiltrating the normal myocardium. Figure 2. Multislice computed tomography axial image of the mass …