Severe motor and intellectual disabilities (SMID) syndrome is a heterogeneous group of disorders with severe physical disabilities and mental retardation. Higher incidence of sudden death is also known in these patients. However, little is known about the cardiovascular features of patients with SMID. We examine the patients with severe motor and intellectual disabilities using echocardiogram and clarify their characterization of ventricular function. We performed electrocardiographic and echocardiographic analyses in SMID patients. In all patients, two-dimensional echocardiography with tissue Doppler analysis in the pulsed Doppler mode was performed. Of 121 patients, 104 patients had abnormal findings: 81 had poor R-wave progression, and 15 patients had low-voltage QRS on ECG. These findings strongly correlated with the degree of physical disability. However, on echocardiography, most patients had LVEF in the normal range, while LV Tei indices were significantly higher (0.43 vs 0.31 cm/s) and left ventricular end-diastolic dimension significantly smaller than healthy controls (P<0.05 for each comparison). Patients had significantly decreased early diastolic tissue Doppler velocities at the lateral mitral (5.3 vs 6.7 cm/s), tricuspid (6.7 vs 9.2 cm/s), and septal (5.9 vs 8.8 cm/s) annuli compared with controls (P<0.05 for each comparison). We show for the first time that SMID patients have low E/Ea ratios on tissue Doppler imaging while LV contractions are normal, suggesting the existence of latent diastolic dysfunction. This may be one of the reasons why the incidence of sudden death is higher in SMID patients.