Cardiovascular diseases such as hypertension, atherosclerosis, cardiac hypertrophy homocysteinemia and arrhythmias impose great health, social and financial costs. Some of these diseases are single gene traits that segregate in a simple Mendelian manner. Most are genetically complex, however, and result from combinations of large numbers of genes (polygenic and epistatic traits) or from interactions between genetic and environmental factors (multifactorial traits). Insights into the genetic control of these diseases could lead to improved diagnosis and treatment as well as a deeper understanding of basic physiological processes.