A cyanotic congenital heart defect
All four<unk>  veins drain into the systemic<unk>  circulation rather than into the left atrium.
Four anatomic forms:
Supracardiac (46%):<unk>  veins connect to the cardinal<unk>  system (left innominate vein, superior vena cava, azygous vein)
Cardiac (20%):<unk>  veins connect to the posterior aspect of the coronary sinus or directly to the right atrium
Infracardiac (23%):<unk>  veins drain into the portal vein, hepatic vein, or IVC
Mixed (11%): Combination of connections that enter at 2 or more levels.
Firth most common cause of cyanotic congenital heart disease 
Supracardiac (46%):<unk>  veins connect to the cardinal<unk>  system (left innominate vein, superior vena cava, azygous vein)
Cardiac (20%):<unk>  veins connect to the posterior aspect of the coronary sinus or directly to the right atrium
Infracardiac (23%):<unk>  veins drain into the portal vein, hepatic vein, or IVC
Mixed (11%): Combination of connections that enter at 2 or more levels.
All oxygenated<unk><unk>  blood mixes with deoxygenated blood from the systemic<unk>  system
Mixed/partially oxygenated blood then shunted right to left (through patent foramen ovale, PDA or an ASD), resulting in cyanosis
The right atrium and ventricle become dilated because the right side of the heart receives blood from both<unk>  and systemic<unk>  systems.
In obstructed forms of<unk> , the<unk><unk>  system is compressed by surrounding structures
May lead to RV hypertrophy and<unk>  vascular changes that may result in RV failure
May lead to RV hypertrophy and<unk>  vascular changes that may result in RV failure
Total anomalous pulmonary venous return
Cyanotic
Transposition of the great arteries
Tetralogy of fallot
Tricuspid atresia
Hypoplastic left heart syndrome
Tetralogy of Fallot
Ebstein anomaly