Reoxygenation following hypoxic episodes can increase the risk for the development of ventricular arrhythmias, which, in addition to circadian aspects of reoxygen ation arrhythmias has not been studied extensively. The aim of the present study was to evaluate circadian changes in the electrical stability of the rat heart during reoxygenation following a hypovent ilatory episode. The electrical stability of the heart, defined in the present study as the ventricular arrhythmia threshold (VAT), was measured at 3 h intervals at clock times 09:00, 12:00, 15:00, 18:00, 21:00, 24:00, 03:00, 06:00 and 09:00 during 20 min hypoventilation (20 breaths/min, tidal volume = 0.5 ml/100 g body weight [n=17]) and subsequent 20 min reoxygenation (50 breaths/min, tidal volume = 1 ml/100 g body weight [n=4]) intervals. The experiments were performed usin g pentobarbital-anesthetized (40 mg/kg intraperitoneally) female Wistar rats that first underwent a four-week adaptation to a 12 h light:12 h dark regimen. Detailed analysis show ed that circadian VATs changed to biphasic rhythms at 10 min of hypoventilation. The VAT circadian rhythms were observed immediately following the commencement of reoxygenation, with the highest values measured between 12:00 and 15: 00, and the lowest values between 24:00 and 03:00. These resu lts suggest that myocardial vulnerability is dependent on the light:dark cycle and characteristics of pu lmonary ventilation., P. Švorc ... [et al.]., and Obsahuje bibliografii a bibliografické odkazy