How does Tetralogy of Fallot come about?

Tetralogy of Fallot (TOF) is a coordinated congenital cardiovascular and cerebrovascular abnormality. TOF includes narrow pulmonary ostium, ventricular septal defect, right pulmonary position and right ventricular hypertrophy. The key to this disease is cyanosis, respiratory failure and hypoxic onset. Squatting is the clinical heteromorphic posture of TOF patients. The key causes are genetic and environmental factors, and viral infection is common among environmental factors.