Tumor lesions of the heart remain an urgent problem due to high mortality. The complexity of early diagnosis of primary cardialymphoma is associated with the non-specificity of symptoms which often leads to the delayed verification of the diagnosis, commonly at stage 4. This article presents a clinical case demonstrating the need for instrumental cardiac diagnostics at an early stage in the presence of non-specific symptoms, such as heart conduction system pathology, hydrothorax, and hydropericardium syndrome.