Background: Magnetic resonance imaging has been demonstrated to be an important non-invasive diagnostic modality in patients with congenital cardiac disease. Few studies, however, have focused on young children. This study examined the clinical utility and technical challenges of cardiovascular magnetic resonance imaging in infants. Methods: All patients aged under 1 year undergoing cardiac magnetic resonance imaging at Boston Children’s Hospital, between January 1999 and July 2002, were identified, and their magnetic resonance imaging records and clinical data were retrospectively reviewed. Results: Cardiac magnetic resonance imaging examinations, 99 in all, were performed in 91 patients with a median weight of 4.9 kg, and a range from 1.2 to 16.3 kg, at a median age of 102 days, with a range from 1 to 358 days. All studies were performed under general anesthesia without any complications, using a head coil in 57, a cardiac scanner in 19, a multi-purpose array in 19, or a surface radio frequency receiver coil of 5 in. in 4. The infants, seen as outpatients, were discharged the same day. The primary questions for referral were delineation of the thoracic vasculature in 54, assessment of possible compression of the airways in 25, evaluation of cardiac tumour in 6, and other reasons in 14. For those referred for assessment of thoracic vasculature, findings at surgery in 37, and catheterisation in 16, were all concordant with the mode for resonance imaging diagnoses. In the children with suspected compression of the airways, findings at surgery in 16, and catheterisation in 2 were also in agreement with findings at resonance imaging. The typing of tumour by resonance imaging in the 3 patients with preoperative studies were all confirmed by pathologic results. Systematic review demonstrated that the anatomy of the airways was best shown with fast spin echo sequences, and the thoracic vasculature by Gadolinium-enhanced 3-dimensional magnetic resonance angiography. Conclusion: Cardiac magnetic resonance imaging plays a limited but important diagnostic role in infants with congenital cardiac disease. It is a useful and safe imaging modality in delineating the thoracic vasculature, evaluating possible compression of the airways, and characterising cardiac tumours. In selected cases, cardiac resonance imaging may obviate the need for cardiac catheterisation or bronchoscopy.