OBJECTIVE To investigate hypoxia and sleep disordered breathing in infants with congenital heart disease. METHODS Prospective study. In-hospital full polysomnography was performed on 14 infants with congenital heart disease, age 7 +/-1 months, and in 7 normal infants, age 10 +/-2 months. Congenital heart disease infants were classified as acyanotic (n=7) or cyanotic (n=7). RESULTS Nutritional status, assessed by the Gomez classification and expressed as % weight for age, was 70 +/-7, 59 +/-11 and 94 +/-16 in the acyanotic, cyanotic congenital heart disease and control infants, respectively (p<0.001). The respiratory disturbance index (AHI, events per hour) was [median (25-75%)]: 2.5 (1.0-3.4), 2.4 (1.5-3.1) and 0.7 (0.7-0.9) in acyanotic, cyanotic CHD infants and controls, respectively (p=0.013). Almost all congenital heart disease infants (11 out of 14) and only one control infant had an AHI >1 event/hour. The minimum oxygen saturation was 79% (74-82), 73% (57-74) and 90% (90-91) in the acyanotic, cyanotic congenital heart disease infants and controls, respectively (p <0.001). The arousal index (events/hour) was similar among the three groups at 8.4 +/-2.4, 10.3 +/-8.7 and 6.5 +/-3, respectively (p=0.451). CONCLUSIONS Infants with congenital heart disease frequently present with sleep-disordered breathing associated with oxygen desaturations but not arousals. Therefore, sleep may represent a significant burden to infants with congenital heart disease.