We wished to determine if obstructive sleep apnea (OSA) is associated with increased left ventricular mass (LVM) and impaired left ventricular diastolic function (LVDF) independently of coexisting obesity, hypertension (HTN), and diabetes mellitus (DM). Patients without primary cardiac disease, referred for evaluation of OSA (n = 533), had overnight polysomnography and Doppler echocardiography while awake. Patients were divided, according to the apnea-hypopnea index (AHI), into an OSA group (AHI > or = 5/h, n = 353) and a non-OSA group (AHI < 5/h, n = 180). In men, LVM was greater in the OSA group (98.9 +/- 25.6 versus 92.3 +/- 22.5 g/m, p = 0.023) despite exclusion of those with HTN and DM. A similar trend was noted in women. Regression analysis revealed that LVM was correlated with body mass index (BMI) (beta = 0.480, p < 0.0005), age (beta = 0.16, p = 0.001), and the presence of HTN (beta = 0.137, p = 0.003) in men and with BMI (beta = 0.501, p < 0.0005) in women, but not with AHI or oxygen saturation during sleep. The ratio of peak early filling velocity to peak late filling velocity (E/A), an index of LVDF, was similar in both groups (1.28 +/- 0.32 versus 1.34 +/- 0.31, p = 0.058); it was correlated with age (beta = -0.474, p < 0.0005), but not with AHI or oxygen saturation during sleep. We conclude that OSA is not associated with increased LVM or impaired LVDF independently of obesity, HTN, or advancing age.