Cardiac involvement in the mucopolysaccharidoses (MPS) and mucolipidoses (ML) was assessed by echocardiography (E) in 32 patients (pts). Standard echocardiograms were examined for asymmetric septal hypertrophy (ASH), mitral and aortic valve abnormalities, and left ventricular (LV) function. 25 pts had MPS and 7 pts had ML. The median age of the group was 7 years (range 15 months - 25 years).ASH (septal:posterior wall thickness ratio ≥ 1.3:1) was found in 20/32 pts (63%) of the total group.Mitral valve abnormalities included a diminished EF slope (<50mm/sec) in 11/32 (34%); decreased CE excursions (<1.5cm) in 23/32 (72%); abnormally thickened chordae in 22/32 (69%); marked flutter in 24/32 (75%) thickened valve in 16/32 (50%). Aortic valve thickening was noted in 9/25 (32%) of the pts with MPS and in none of the pts with ML. LV function as determined by ejection fraction, VCF, ΔP, and systolic time intervals vas normal in all but 2/32 (6.2%) pts.In summary, the spectrum of cardiac lesions in MPS and ML, was demonstrated by E. In addition to previously described valvular involvement, we have demonstrated gross septal hypertrophy, presumably a result of myocardial deposition. Surprisingly, LV function was not depressed in our series. However, serial studies are indicated for signs of progressive myocardial dysfunction.