We present a case of total anomalous pulmonary venous drainage. Despite low oxygen saturation an eight-week-old girl had only minimal symptoms initially. She suffered collapse requiring acute surgical correction and prolonged intensive care. Her collapse and complicated post-operative course could have been avoided with earlier diagnosis. Infants with critical heart disease continue to be born undiagnosed despite prenatal ultrasound screening. There is evidence that infants with critical congenital heart defect can be detected by pulse oximetry screening, as is routine in Norway, Sweden and Finland, but not in Denmark.