Primary cardiac lymphomas are extremely rare and make up only 1% to 2% of primary cardiac tumors. Due to their rarity, the diagnosis is usually delayed and often made post-mortem. Cardiac lymphomas have been reported in immunocompromised individuals (HIV+; transplant recipients). These patients tend to be younger with a striking male predominance. Sporadic cases involve older immunocompetent individuals. Most primary cardiac lymphomas are diffuse large B-cell lymphomas (DLBCL). The example shown here is composed of diffuse sheets of centroblasts with a few reactive lymphocytes (usually T-cells) and macrophages in the background. Mitotic activity is high.