Failure of the tricuspid valve to develop, preventing blood from entering the right ventricle from the right atrium

Deoxygenated blood shunts from the right atrium through an atrial septal defect or a patent foramen ovale to the left atrium, where it mixes with oxygenated blood.

Mixed blood then passes to the left ventricle through a ventricular septal defect to the right ventricle, pulmonary artery, and lungs; or, mixed blood from the aorta refluxes back through a patent ductus arteriosus to the lungs.

Unknown

May be associated with pulmonic stenosis or transposition of the great vessels