The CPAP-therapy is the most effective treatment in patients with obstructive sleep apnea syndrome so far, counteracting intermittent hypoxia. Despite the previously observed reduction of the heartrate, to date only a few studies have dealt with this subject-matter specifically. Therefore, this thesis focuses on the influence of the CPAP-therapy on the heartrate in patients with obstructive sleep apnea syndrome. The analysis of the retrospectively collected data confirms a low, but significant reduction of the heartrate. This reduction plays a crucial role decreasing the risk of secondary cardiovascular disease. Any additional influence of the exploratory parameters could not be ruled out in this context.