Determination of the situs of the aortic arch is extremely important in the complete evaluation of infants with congenital heart disease, as well as in infants with esophageal atresia and tracheoesophageal fistula in whom the thoracotomy incision is performed contralateral to the aortic arch.1 Definitive determination of the side of the aortic arch can be made angiographically, but this is invasive and requires transport of the infant. The thoracic roentgenogram is not always reliable in determining aortic arch situs, particularly in newborns. Computed tomography of the thorax has also been used,2 but tomographs are not portable. Evaluation of the aortic arch from the suprasternal notch using cardiac ultrasound has been reported.3-6 In most studies, the sector orientation required for a long-axis image of the arch was used to distinguish situs.3-5 The position of the descending thoracic aorta also has been used to infer the side of the aortic arch.4-5 These techniques are subjective and depend on the skill of the operator. They do not provide for a descending aorta contralateral to the aortic arch with retroesophageal segment, nor for cardiac malpositions. The relative positions of the esophagus and aortic arch have also been used to identify the side of the arch,6 but this technique is not useful with esophageal atresia. We therefore devised a new technique to evaluate aortic arch situs from a parasternal short-axis approach.