We describe a neonate who presented with an echogenic mass in the right atrium 8 weeks after closure of ventricular and atrial septal defects. On a routine post operative check up after discharge, a mass was detected in the right atrium on echocardiography. As a thrombotic formation was suggested, lysis was started, in combination with the administration of unfractioned heparin. As there was no change in echogenicity or size of the mass, it was surgically excised. Histopathological examination revealed a myofibroblastic inflammatory tumour.