Two cases of cardiac rhabdomyoma discovered fortuitously at foetal ultrasonography gave rise to no obstructive cardiac signs or arrhythmias either in the antenatal or postnatal periods. These multiple tumours often observed in Bourneville's tuberous sclerosis orientated the clinical investigations to the diagnosis of this disease from the outset. MRI demonstrated cortical tubers and subependymal nodules in both cases. A retinal hamartoma was present in one case. No renal involvement could be detected by ultrasonic examination. No neurological or cardiovascular symptoms appeared during follow-up (20 and 4 months after birth). Investigations in the parents were negative, these two cases being sporadic forms of Bourneville's tuberous sclerosis. The functional prognosis is related to the neurological outcome. Doppler echocardiography would appear to be the best method of following up cardiac rhabdomyomas, and enabled the demonstration of partial regression of the largest tumour in one of these two cases. Cardiac MRI is also an excellent diagnostic tool. As it is usually performed at the same time as cerebral MRI, essential in the follow-up of Bourneville's tuberous sclerosis, it does not represent additional discomfort to the patient.