The Sleep Apnea Syndrome is a common disease in middle- aged patients.Extreme bradycardia with ventricular asystole lasting >10 seconds has been well described in these patients. To date however, it is still unknown whether fixed or anatomic abnormalities of the sinus node and the atrioventricular (AV) conduction system have a role in the genesis of ventricular asystole during obstructive sleep apnea. This study assesses electrophysiologic parameters of sinus node function and AV- conduction before and after administration of atropine in patients with prolonged ventricular asystole occuring exclusively during obstructive sleep apnea. Method: A total of 22 patients (20 men and 2 women; age:47,1 y; BMI:38,2KG/m2; Apnea/Hypopnea Index: 73,7/h) with ventricular asystole occuring exclusively during obstructive sleep apnea on diagnostic polysomnography with simultaneous 2-channel Holter monitoring were recruited from the Marburger Sleep Disorder Clinic. In addition to full- night polysomnography and 24- hour Holter monitoring, the patients got an electrophysiologic evaluation. Results:Parameters of Sinus node function were completely normal in 20 patients (91%).After atropine administration it normalized in the other 2 patients. AH-Intervalls, AV- block cycle length and AV node recovery time were normal in 18 patients (82%). In 2 patients AH- intervals and AV. block cycle length were prolonged, but normalized after atropine administration. Discussion: The present study is so far the biggest collectiv of patients with OSA and Bradycardia during OSA, who was assessed with Electrophysiologic Evaluation. It revealed normal electrophysiologic findings of sinus node function and AV conduction time in most patients. Mildly abnormal findings were reversible by administration af atropine in almost all patients, which suggests enhanced vagal tone rather than structural abnormalities of the sinus and AV nodes as the underlying mechanisms of these findings.