OBJECTIVE: A common arterial trunk is a solitary trunk that exits the heart through a common ventriculo-arterial junction and supplies directly the systemic, pulmonary, and coronary arterial pathways. It remains to be determined, however, how best to subclassify those hearts fulfilling this definition. The time-honored classification is based on the morphology of the pulmonary arteries, but an alternative approach also places emphasis on the nature of the systemic pathways. We evaluated our experience to establish whether these different approaches can be reconciled. METHODS: We examined 28 autopsied hearts with common arterial trunks; the specimens were drawn from the archives of three institutions. Based on our analysis, we simplified classification into hearts with aortic or pulmonary dominance. We used this approach to categorize 42 patients who had undergone surgical correction at Children's Memorial Hospital in Chicago. RESULTS: All autopsied hearts could be assigned to groups with either aortic or pulmonary dominance of the common arterial trunk, with 20 and 8 specimens, respectively, fitting into these categories. Pulmonary dominance was found only when the aortic component of the trunk was hypoplastic and an arterial duct supplied the majority of flow to the descending aorta. Only in this setting did we observe pulmonary arteries arising from the sides of the major pathway, and only in this setting was the aortic component discrete from the pulmonary component within the pericardial cavity. CONCLUSIONS: This simple approach to classification reconciles the existing disparate categorizations of patients having common arterial trunks and it emphasizes the principal morphologic determinant of surgical outcome.