[7] When present, symptoms are variable and may include rapid breathing, bluish skin (cyanosis), poor weight gain, and feeling tired.

[4] Risk factors include certain infections during pregnancy such as rubella, use of certain medications or drugs such as alcohol or tobacco, parents being closely related, or poor nutritional status or obesity in the mother.

[15] Some children have no signs while others may exhibit shortness of breath, cyanosis, fainting,[16] heart murmur, under-development of limbs and muscles, poor feeding or growth, or respiratory infections.

Mutations of a heart muscle protein, α-myosin heavy chain (MYH6) are associated with atrial septal defects.

The Wnt signaling co-factors BCL9, BCL9L and PYGO might be part of these molecular pathways, as when their genes are mutated, this causes phenotypes similar to the features present in Holt-Oram syndrome.

[27] The notch signaling pathway, a regulatory mechanism for cell growth and differentiation, plays broad roles in several aspects of cardiac development.

Notch elements are involved in determination of the right and left sides of the body plan, so the directional folding of the heart tube can be impacted.

Notch signaling is involved early in the formation of the endocardial cushions and continues to be active as the develop into the septa and valves.

Mutations in the gene for one of the notch ligands, Jagged1, are identified in the majority of examined cases of arteriohepatic dysplasia (Alagille syndrome), characterized by defects of the great vessels (pulmonary artery stenosis), heart (tetralogy of Fallot in 13% of cases), liver, eyes, face, and bones.

[32] Known environmental factors include certain infections during pregnancy such as rubella, drugs (alcohol, hydantoin, lithium and thalidomide) and maternal illness (diabetes mellitus, phenylketonuria, and systemic lupus erythematosus).

[35] A distinct physiological mechanism has not been identified to explain the link between maternal obesity and CHD, but both pre-pregnancy folate deficiency and diabetes have been implicated in some studies.

[37] A systematic review and meta-analysis of four studies conducted in 2007 showed a 9-fold increase in CHD risk in MC twins compared to singletons.

[39] At day 22, the circulatory system is bilaterally symmetrical with paired vessels on each side and the heart consisting of a simple tube located in the midline of the body layout.

The main outflow tract is divided in two by the growth of a spiraling septum, becoming the great vessels—the ascending segment of the aorta and the pulmonary trunk.

A small vessel called the ductus arteriosus allows blood from the pulmonary artery to pass to the aorta.

The two flaps may fuse, but many adults have a foramen ovale that stays closed only because of the pressure difference between the atria.

[citation needed] If a baby is born with cyanotic heart disease, the diagnosis is usually made shortly after birth due to the blue colour of their skin (called cyanosis).

In 2000 the International Congenital Heart Surgery Nomenclature was developed to provide a generic classification system.

[46] Obstructive defects occur when heart valves, arteries, or veins are abnormally narrow or blocked.

[49] Cyanotic heart defects are called such because they result in cyanosis, a bluish-grey discoloration of the skin due to a lack of oxygen in the body.

Such defects include persistent truncus arteriosus, total anomalous pulmonary venous connection, tetralogy of Fallot, transposition of the great vessels, and tricuspid atresia.

Medications include diuretics, which aid the body in eliminating water, salts, and digoxin for strengthening the contraction of the heart.

Some defects require surgical procedures to restore circulation back to normal and in some cases, multiple surgeries are needed.

[citation needed] Interventional cardiology now offers minimally invasive alternatives to surgery for some patients.

The Melody Transcatheter Pulmonary Valve (TPV), approved in Europe in 2006 and in the U.S. in 2010 under a Humanitarian Device Exemption (HDE), is designed to treat congenital heart disease patients with a dysfunctional conduit in their right ventricular outflow tract (RVOT).

[52] For congenital heart defects that arise without a family history (de novo), the recurrence risk in offspring is 3–5%.

[53][54] This risk is higher in left ventricular outflow tract obstructions, heterotaxy, and atrioventricular septal defects.