Congenital heart defects in malformation syndromes. This article presents a comprehensive review of the type and frequency of congenital heart defects found in malformation syndromes which have been categorized by etiology. Certain cardiac phenotypes can be as helpful in identifying certain syndromes as can be seen with the more familiar facial, body, and behavioral phenotypes. An awareness of syndromes with a higher risk of congenital heart defect, and knowledge concerning heart defects which are distinctive for certain syndromes, focuses prenatal diagnosis efforts and fetal echocardiography. By using a mechanistic classification in which congenital heart defects are regarded as families of related defects rather than individual lesions, patterns can be recognized among different syndromes. 