The studies summarized demonstrate that CHD is a common, major malformation. The genetic cause of each specific lesion is heterogeneous. In addition, different types of CHD can result from the same chromosomal alteration or from mutations in the same gene. Although one might predict that genotype influences clinical outcome, further studies are required. At this time, routine clinical diagnostic tests to identify the specific genetic cause are available in only a few cases, namely, those with abnormal karyotypes or those with a 22q11 deletion. In those cases with single-gene defects, genetic testing is not clinically available at this time and most likely will not become available until we can predict the significance of each mutation and until technologic advances are made that allow for large-scale, accurate screening. In the meantime, continued research on the genetic cause of CHD promises to augment our understanding of the mechanisms underlying the normal and abnormal development of the cardiac structures. These investigations also promise to augment our ability to counsel families on the recurrence risk with greater accuracy and, in the future, will allow the physician to modify his or her clinical management based on genetic cause. Finally, identifying the cause and understanding the disease mechanism allows for early intervention that may modify the degree of cardiac maldevelopment or avoid cardiac malformation altogether.