Patients with cardiovascular disease, like other patient groups, vary in their response to drugs. This is true both in terms of the response of their disease to treatment and their ability to tolerate medication. Several factors contribute to this variability, including diVerences in body mass, co-existent renal disease, concomitant drug treatment, and the heterogeneous nature of the disease. The Human Genome Project and the general focus of clinical science on genetic determinants of disease has increased interest in the role of genetic factors in determining an individual’s response to drugs. Pharmacogenetics is a growing discipline concerned with the eVect of genetic variation on the response to drugs and the extent to which drug treatment can be tailored to the individual according to their genetic makeup.