We investigated return of spontaneous circulation and of cerebral oxygenation after asphyxia-induced cardiac arrest, using ventilation with air, throughout, or with 100% oxygen for a shorter or longer period. Arterial pressure, heart rate, regional cerebral oxygen saturation (CrSO2), and brain tissue oxygen tension (PbtO2) were measured in 1-d-old piglets that were hypoventilated with air and left in apnea until cardiac arrest. They were randomly assigned to be resuscitated with air (n = 13), or with oxygen for 3 (n = 12) or 30 min (n = 13) and then with air. Nine, 10, and 10 animals, respectively, needed closed chest cardiac massage. One, none, and one, respectively, died. Median (quartile range) times from start of ventilation until heart rate reached 150 bpm were 67 (60-76), 88 (76-126), and 68 (56-81) s. They were not significantly different, nor were the arterial pressure responses, times until CrSO2 reached 30%, or times until PbtO2 had increased by 0.1 kPa from its nadir. Peak PbtO2 values during resuscitation were 4.2 (3.3-5.4), 12 (6.4-15), and 25 (15-36) kPa. Thus, pure oxygen did not accelerate the recovery of circulation or of cerebral oxygenation, while even a brief exposure caused cerebral hyperoxia.