In order to study the prevalence of cardiac rhabdomyoma in tuberous sclerosis using non invasive methods, 11 consecutive patients affected by tuberous sclerosis (age: 3 months-22 years, mean 6 years) were examined between January 1984 and April 1987. In each patient clinical examination, 12 lead electrocardiogram, M-mode and two-dimensional echocardiogram were performed: on 7 of them a 24-hour ambulatory electrocardiogram was also performed. Clinical examination revealed a systolic murmur (grade 3/6) in two cases. In one of them it was associated with cyanosis and cardiac failure. None of other patients showed signs or symptoms related to the heart during clinical examination. ECG was abnormal in 3 cases (ventricular pre-excitation in 2 cases and left ventricular strain in 1). Two-dimensional echocardiogram showed single or multiple intracardiac masses suggestive of cardiac rhabdomyoma in 8 cases; in 3 of them masses were isolated, intramural, and in the interventricular septum, from 5 to 16 mm in diameter; in the other 5 cases they were multiple, intramural and endoluminal, in the interventricular septum, in the right or left ventricle, from 7 to 20 mm in diameter. Ambulatory electrocardiogram revealed only isolated ectopic supraventricular and ventricular beats in 2/7 cases. Each patient was clinically controlled every six months using ECG standard and two-dimensional echocardiogram. The mean follow-up period was 32 months (range 9-53). This study confirms the usefulness of the two-dimensional echocardiography to visualize intramural or intracavitary masses due to cardiac rhabdomyoma in patients with tuberous sclerosis, especially when they appear clinically asymptomatic. Two-dimensional echocardiography is probably the ideal method to use in order to evaluate potential increase in cardiac rhabdomyoma, when prolonged follow-up studies are performed.