The study of sleep, which initially focused on the neurophysiological mechanisms and cardiorespiratory function during the night, has shown the presence of sleep-related breathing disorders that epidemiological, pathophysiological and clinical data have indicated to be associated with increased cardiovascular morbidity and mortality: the obstructive sleep apnea syndrome (OSAS) and the central sleep apnea syndrome (CSAS). OSAS is a condition characterized by repetitive respiratory pauses due to the pharynx wall collapse, with a subsequent obstruction to the airflow. The hemodynamic consequences due to the markedly increased negative intrathoracic pressure (induced by the respiratory muscle effort towards the closed upper airways), the progressive hypercapnic hypoxemia and the arousal terminating the apneas, are the pathophysiological keys of the cardiovascular effects of OSAS and may explain the association between OSAS and the documented increase of cardiovascular morbidity and mortality. CSAS is a breathing disorder characterized by recurrent episodes of central hypopneas or apneas and hyperventilation which, is the classical form described by Cheyne and Stokes, show a crescendo-decrescendo pattern of respiration. Pathophysiological and epidemiological data clearly indicate the link between CSAS and heart failure, also showing a correlation between respiratory disorders and the severity of hemodynamic impairment. However, other mechanisms are involved in the genesis of CSAS in explaining the variable presence of CSAS independent of cardiac function and, more importantly, the impact of CSAS on poor prognosis in heart failure. In conclusion, the data available indicate the need to include screening for sleep-related breathing disorders in the evaluation of cardiac patients who are at risk for OSAS and, particularly, in patients with heart failure, who could really benefit from treatment of the respiratory disorder.