Atrioventricular septal defect (AVSD) or atrioventricular canal defect (AVCD), also known as "common atrioventricular canal" (CAVC) or "endocardial cushion defect" (ECD), is characterized by a deficiency of the atrioventricular septum of the heart that creates connections between all four of its chambers. It is caused by an abnormal or inadequate fusion of the superior and inferior endocardial cushions with the mid portion of the atrial septum and the muscular portion of the ventricular septum. Symptoms and signs Symptoms include difficulty breathing (dyspnea) and bluish discoloration on skin, fingernails, and lips (cyanosis). A newborn baby will show signs of heart failure such as edema, fatigue, wheezing, sweating and irregular heartbeat. Complications Normally, the four chambers of the heart divide oxygenated and de-oxygenated blood into separate pools. When holes form between the chambers, as in AVSD, the pools can mix. Consequently, arterial blood supplies become less oxygenated than normal, causing ischemia and cyanosis in distal tissues. To compensate, the heart must pump a larger volume of blood to deliver enough oxygen, leading to cardiac enlargement and hypertrophy. The development of pulmonary hypertension is very serious. And this because the left ventricle is weakened due to its overuse. When this happens, the pressure backs up into the pulmonary veins and the lungs. This type of damage is irreversible which is why immediate treatment is recommended after diagnosis. Associated conditions Down syndrome is often associated with AVCD. Other risk factors include: having a parent with a congenital heart defect, alcohol use while pregnant, uncontrolled diabetes treatment during pregnancy and some medications during pregnancy. This type of congenital heart defect is associated with patients with Down syndrome (trisomy 21) or heterotaxy syndromes. 45% of children with Down syndrome have congenital heart disease. Of these, 35–40% have AV septal defects. Approximately 40-50% of fetuses diagnosed with AVCD have Down syndrome, and a further 15-20% are associated with other chromosomal abnormalities and syndromes, such as DiGeorge syndrome. The remaining 30-40% of cases are not linked to a syndrome, with AVCD observed without other major defects. AVCD is also linked with Noonan syndrome. The pattern seen in those patients with Noonan syndrome differ from those patients who have Down syndrome in that "partial" AVCD is more prevalent in those with NS, whereas those with down syndrome show a prevalence of the "complete" form of AVCD. Pathophysiology Defective embryonic formation of the heart results in multiple holes between the