Background/Aims: Arterial hypertension is frequently associated with sleep apnea, excessive weight, and with changes in the echocardiographic characteristics of the left cardiac chambers. The present investigation was conducted in order to search for a possible relation between left cardiac structure and sleep apnea magnitude in patients with arterial hypertension and excessive weight. Methods: A group of 56 patients with arterial hypertension and mean body mass index of 30.6 ± 3.8 (weight in kilograms/height in meters squared) was studied by echocardiography, sleep study and electrocardiography. Results: A relatively high mean apnea-hypopnea index (AHI) was found (17.9 ± 17.2 episodes/h sleep), but this parameter was not found to be correlated with cardiac echocardiographic diameters. Patients with an AHI <5 episodes/h had smaller mean values for left atrial diameter, left ventricular mass index and left ventricular relative wall thickness, when compared to patients with an AHI value of ≧5. The mean corrected QT interval was found to be longer in female patients, whereas left ventricular end-diastolic diameter was smaller than in male patients. Conclusion: In patients with arterial hypertension and excessive weight, significant apnea seems to be very common. In such patients, left ventricle wall thickness, left ventricle mass index and the left atrium diameter may act as surrogate markers for significant sleep apnea. Thus, the hypothesis is raised that hypoxia may lead to changes in heart structure.