The purpose of this report is to present the findings in a neonate with tetralogy of Fallot and a history of prolonged sleep-related apnea requiring resuscitation. At a baseline arterial oxygen pressure of 46 mm Hg, his preoperative responses to carbon dioxide during non-REM sleep (26.1 and 26.6 ml/kg/min/mm Hg of alveolar carbon dioxide tension [PACO2]) were identical to those reported in near-miss sudden infant death syndrome. Following a systemic-pulmonary arterial shunt, the arterial saturation reached 95 percent, and no further apnea occurred. The prompt normalization of the response to carbon dioxide following surgery (75.2 and 75.4 ml/kg/min/mm Hg of PACO2) indicates that, unlike infants with the sudden infant death syndrome, a low sensitivity to carbon dioxide in infants with cyanotic heart disease may be dependent on hypoxemia and, thus, reversible.