The pathogenesis of most cardiovascular disorders is multifactorial and incompletely understood. Besides genetic influences that often arise from multiple genetic loci, the specific nutritional and environmental influences do contribute to the dysfunctional development. Nevertheless, a rather small number of cardiovascular diseases exhibits Mendelian traits, since they are caused by a single gene defect. Examples are familial cardiomyopathies, primary arrhythmias and connective tissues disorders of vessels. More detailed investigations reveal that even these entities are usually not purely monogenic, as they do not appear with the same intensity in all mutation carriers. Hence, there must be further modifying factors that influence the penetrance of the disease. Despite this limitation monogenic diseases allow the identification of the underlying genetic defects and thereby a deeper insight into the pathophysiology. Predictive genetic diagnostics, on the other hand, permit a better adaptation of medical care to the individual risk of offspring that are not yet affected.