Primary tumours of the heart are extremely rare. Sarcomas are considered to be the most frequent histological type. This study presents two cases with a two-week and two-month history of fatigue, fever and shortness of breath. In both cases, cardiac tumours with pericardial effusion were diagnosed by means of echocardiography, being responsible for the above-mentioned symptoms. At the beginning of the diagnostic process, sarcomas seemed to be the likeliest cause of these symptoms. Establishment of the histopathological diagnosis based on the tumour biopsy turned out to be very difficult, and this delayed further therapeutic procedures.