Right atrial myxoma was thought in one of the two male patients ages 4.5 and 7 years old due to right atrial mass detected by echocardiography during their admission to our clinic with right cardiac insufficiency. The mass was extirpated with open heart surgery and found out that it was an extention a wilm's tumour. With further investigation the primary tumour was found in the left kidney and a nephrectomy was done subsequently. Another 7 years old patient also had a Wilms' tümör history 6 months ago and a right atrial mass was also found by echocardiography and extirpated by on open heart surgery. Both patients received radiotherapy and chemotherapy and alive for 2 years. Although this cardiac mass necessitated urgent open heart surgery, the prognosis of the cases were identical to stage II Wilms' tumour cases.