Primary cardiac lymphoma, an extremely rare type of B-cell non-Hodgkin lymphoma, has an incidence of approximately 0.02-2% among malignant cardiac tumors. It is frequently associated with manifestations such as cardiac rhythm disturbances, refractory pericardial effusion and cardiac masses. Definitive diagnosis is achieved by biopsy, being essential to rule out hematogenous dissemination with PET-CT. The literature indicates a predominance of right chamber involvement and survival that varies significantly according to left ventricular involvement and the presence of arrhythmias. Therapeutic options are not well defined, but chemotherapy such as R-CHOP has shown efficacy, although the prognosis is generally poor due to complications such as disease progression, arrhythmias and sepsis. This case underscores the importance of considering cardiac lymphoma in patients with unexplained cardiac symptoms, highlighting the need for a multidisciplinary and specific diagnostic and therapeutic approach.