These malformations include ventricular septal defect (VSD); patent ductus arteriosus (PDA); atrial septal defect (ASD); partial anomalous pulmonary venous connection (PAPVC), with or without ASD; atrioventricular canal (AVC) malformations; and aortopulmonary fenestration (AP window). The hemodynamic abnormalities are the result of left-to-right shunting and correlate with the degree of the shunt. Neonates, who have high pulmonary vascular resistance, generally have a small and clinically insignificant left-to-right shunt. During the first few days and weeks, as the pulmonary vascular resistance falls, the left-to-right shunting may increase and heart failure may ensue. Physiologically, this failure represents diastolic overload to the left ventricle, with increased pulmonary blood flow and pulmonary hypertension as noted in VSD, complete AVC or transitional AVC with large VSD, PDA, and AP window. Aortic runoff results in low diastolic pressure and increased pulse pressure (bounding pulses) and is found with PDA and AP window. AP windows are rare. ASDs cause right ventricular diastolic overload and do not usually cause congestive heart failure in children. During the childhood years, pressure overload is required to cause heart failure in the volume-overloaded right ventricle. Long-standing high flow and high pressure in the pulmonary vascular bed result in injury to the small pulmonary arteries and arterioles and the development of pulmonary vascular obstructive disease (PVOD). In advanced PVOD, the pulmonary vascular resistance approaches or exceeds the systemic resistance and causes reversal of the shunt (right-to-left shunting), with resulting cyanosis, hypoxemia, erythrocytosis, and increased blood viscosity.

Outflow obstruction may occur at the right or left ventricular outflow tracts and at or distal to the semilunar valves. These anomalies include pulmonic valve stenosis and aortic valve stenosis, subpulmonic stenosis and subaortic stenosis, pulmonary artery stenosis, supravalvar aortic stenosis, and coarctation of the aorta. The hemodynamic abnormalities result from systolic overload of the right or left ventricles. The severity of the disease correlates with the systolic pressure in the ventricle and the systolic pressure gradient across the obstruction. The systolic overload is compensated by maintaining wall stress by developing hypertrophy, which when severe, however, results in decreased compliance of the ventricle and abnormal ventricular function. The clinical findings of obstruction at the semilunar valves or at the ventricular outflow tracts are highlighted by outflow murmurs. In supravalvar aortic stenosis there is a significant systolic pressure gradient between the two arms, with the right arm systolic pressure higher than that in the left arm. The presence of a large systolic pressure difference between the upper and lower extremities, with systemic hypertension of the arms and delayed and barely palpable arterial pulsations in the legs, is diagnostic of coarctation of the aorta.

Cardiomyopathies, which may be hypertrophic or dilated (congestive), are uncommon anomalies. Hypertrophic cardiomyopathies can be obstructive and result in left ventricular outflow obstruction or can be nonobstructive, as in nonobstructive asymmetric septal hypertrophy and concentric left ventricular hypertrophy. Ventricular noncompaction cardiomyopathy, which is the result of arrest in normal process of myocardial compaction in the fetal life, is an uncommon cardiomyopathy involving left ventricle and rarely right ventricular myocardium and ventricular septum. Left ventricular noncompaction presents as an isolated anomaly or in association with other cardiovascular malformations. Anomalous origin of the left coronary artery arising from the main pulmonary artery results in anterolateral myocardial infarction and is grouped under the congestive cardiomyopathies.

Complete transposition of the great arteries (d-TGA), which is the most common cyanotic heart disease of neonates, is anatomically signified by the aorta arising from the outflow of the right ventricle and the pulmonary artery from the left ventricle, resulting in severe hypoxemia. Unlike the normal circulation, in which the pulmonary and systemic circuits work in series, in d-TGA, the two circuits function in parallel. This anomaly is incompatible with life unless mixing of systemic and pulmonary venous blood becomes possible by the presence of an additional cardiac defect (ASD, VSD, or common ventricle). An ASD can be created by balloon atrial septostomy (BAS). BAS is an effective method of treatment in neonates while waiting for surgical correction. The Mustard and Senning operations redirect the pulmonary and systemic venous returns and offer a functional correction. The Jatene procedure offers correction by aorta and pulmonary arterial switch.

Anomalies in this category include tricuspid atresia, pulmonary atresia or critical pulmonic valve stenosis with intact ventricular septum, tetralogy of Fallot (right ventricular outflow obstruction with VSD and overriding aorta), severe Ebstein malformation of the tricuspid valve (adherence of redundant tricuspid valve leaflets to the right ventricular walls resulting in tricuspid regurgitation, small right ventricular cavity, and decreased forward flow), common ventricle (univentricular heart), and double-outlet right ventricle with pulmonary atresia or severe pulmonic stenosis. Severe hypoxemia results from critically decreased pulmonary blood flow and is exaggerated by right-to-left shunting at the atrial level through an ASD or patent foramen ovale or at the ventricular level through a VSD. Immediately after birth, pharmacologic palliation is indicated with prostaglandin E₁ to keep the ductus arteriosus patent while planning for surgical palliation by systemic-to–pulmonary artery shunt (modified Blalock-Taussig shunt with interposing graft between subclavian artery and pulmonary artery or aorta to pulmonary artery shunt by interposition graft), until more definitive surgery is performed.

The mixture of pulmonary and systemic venous blood results in unrestricted large pulmonary blood flow and smaller, usually restricted, systemic blood flow. These anomalies include total anomalous pulmonary venous connection, common ventricle (univentricular heart) and double-outlet right ventricle without pulmonary atresia or severe subpulmonic and pulmonic valve stenosis, persistent truncus arteriosus, and hypoplastic left heart syndrome. Because of markedly increased pulmonary blood flow, hypoxemia and cyanosis are moderate in severity, and congestive heart failure and systemic hypoperfusion dominate the clinical picture. Intensive medical treatment with inotropic and diuretic drugs is indicated. Early surgical palliation or correction is required.