A 73-year-old woman presented in right heart failure. Computed tomography of the chest revealed a 3 cm × 5 cm anterior mediastinal mass. Contrast-enhanced two-dimensional transthoracic echocardiography, cardiac magnetic resonance imaging (MRI), positron emission tomography (PET), and MRI–PET fusion demonstrated invasion of the pericardium and right heart by the tumor. Mediastinal biopsy revealed high-grade diffuse large B-cell lymphoma, which responded to chemotherapy. The role of each modality in this case was discussed in the manuscript. In conclusion, the integration of multiple imaging modalities is extremely useful in the characterization, localization, diagnosis and treatment of an unusual cardiac mass.