• According to Clark (2002) classification, there are six causative mechanisms (1) ectomesenchymal tissue migration abnormalities (causing conotruncal malformations and aortic arch anomalies); (2) intracardiac blood flow defects (causing septal defects and left or right heart obstructive malformations); (3) cell death abnormalities (causing septal defects and valve abnormalities); (4) extra cellular matrix abnormalities (causing atrioventricular canal defects); (5) abnormal targeted growth (causing partial or total anomalous pulmonary venous return and cor triatriatum) and (6) abnormal situs and looping (causing left–right positioning problems)Cardiovascular malformation are potentially dangerous in two ways, first, they may produce arteriovenous shunts which put the circulation at a mechanical disadvantage, in some cases so much blood bypasses the lungs that the infant is cyanotic even at rest, secondly, one or more of the heart channels may be narrowed as to cause congestive heart failure in childhood or render mechanically stressed areas of the endocardium susceptiable to blood-born disease for example, bacterial endocarditis may results from dental or tonsillar infections.