Background Pacemaker infections rates are high compared with the incidence of primary malignant cardiac tumors. However, they can look alike in diagnostics and patient presentation. Case Description We hereby report a rare case of a suspected pacemaker endocarditis which in fact turned out to be a primary cardiac B cell lymphoma. The lymphoma was removed surgically. Conclusion Sometimes we encounter the unexpected. Suboptimal preoperative diagnostics certainly lead to the faulty conclusion of an endocarditis. Nonetheless, even such an enhanced primary cardiac tumor can be resected with good clinical outcome and long-term survival.