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Severe obstruction to systemic arterial blood flow, the most common cause of heart failure in the newborn, causes inadequate systemic perfusion and multiorgan failure. Obstruction may be at any one of several locations from the pulmonary veins to the aorta. Specific conditions include obstructed total anomalous pulmonary venous return, mitral atresia or severe stenosis, aortic atresia or severe stenosis, interruption of the aortic arch and severe coarctation of the aorta. Age of onset and severity of symptoms can vary, depending upon precise anatomy and physiology. Time of closure of the ductus arteriosus plays a particularly crucial role in these left heart obstructions, as patency of the ductus can continue to provide systemic blood flow from the right ventricle as it did prior to birth.