Pericardial effusion (PE) can occur in inflammatory and infectious diseases; postoperatively, in pulmonary arterial hypertension, renal failure, as well as in malignant diseases that can affect the pericardium and manifest as a paraneoplastic syndrome (1). On the other hand, the presence of blood in the pericardial cavity – hemopericardium – is more commonly seen in aortic dissection, cardiac rupture, trauma, or after invasive procedures (2) and less frequently in malignant cardiac tumors. The late diagnosis of content in the pericardial cavity, often due to the absence of specific symptoms, can lead to delayed detection and preclude radical treatment in the case of tumors or neoplastic heart lesions. However, early diagnosis and tumor resection can significantly improve patients' condition and allow for life-extending chemotherapy (3). This case highlights the critical importance of early detection in pericardial effusion. The purpose of presenting this clinical case is to increase awareness and alertness among family doctors, therapists, cardiologists, cardiothoracic surgeons, and radiologists to exclude neoplastic involvement of the heart when hydro- or hemopericardium is detected.