Hemitruncus arteriosus (HA) is an uncommon congenital cardiac malformation in which one pulmonary artery branch originates from the ascending aorta. A 2-month-old male was referred to our hospital for failure to thrive, cyanosis, and tachypnea. A chest radiograph demonstrated moderate cardiomegaly and peribronchial thickening. Echocardiography demonstrated right atrial and ventricular enlargement and increased gradient (25mmHg) in the right pulmonary artery. Cardiac magnetic resonance angiography was performed and clearly revealed typical imaging findings of a right HA which had complex cardiac and vascular anatomy. This case report presents cardiac magnetic resonance angiography findings of HA. © 2012 Wiley Periodicals, Inc.