The aim of this study was to characterize cardiovascular involvement in a large number of patients with LEOPARD syndrome. Twenty-six patients (age range 0 to 63 years, median age at the time of the study evaluation 17 years) underwent clinical and genetic investigations. Familial disease was ascertained in 9 patients. Nineteen patients (73%) showed electrocardiographic abnormalities. Left ventricular (LV) hypertrophy was present in 19 patients (73%), including 9 with LV outflow tract obstructions; right ventricular hypertrophy was present in 8 patients (30%). Valve (57%) and coronary artery (15%) anomalies were also observed. Single patients showed LV apical aneurysm, LV noncompaction, isolated LV dilation, and atrioventricular canal defect. During follow-up (9.1 +/- 4.5 years), 2 patients died suddenly, and 2 patients had cardiac arrest. These patients had LV hypertrophy. Despite the limited number of subjects studied, genotype-phenotype correlations were observed in familial cases. In conclusion, most patients with LEOPARD syndrome showed LV hypertrophy, often in association with other valvular or congenital defects. A spectrum of underrecognized cardiac anomalies were also observed. Long-term prognosis was benign, but the occurrence of 4 fatal events in patients with LV hypertrophy indicates that such patients require careful risk assessment and, in some cases, consideration for prophylaxis against sudden death.