The completion of sequencing of the human genome will be the vanguard for numerous advances in medicine. The first discernible application is likely to occur in pharmacogenomics, a field focused on the influence of genetic differences on the variability in patients' response to medications. While an inherited basis for drug response has been recognized for some time, it is the confluence of molecular biology, high-throughput genotyping, and bioinformatics that has made it practical to study the genetic basis of variability to medications on a large scale. Pharmacogenomics may enable clinicians to prospectively identify patients most likely to derive benefit from a drug, with minimal likelihood of adverse events. This DNA-based approach to predicting clinical drug efficacy and toxicity would shift the current prescribing paradigm from its empirical nature to a more patient-specific model, ushering in a new era of personalized medicine. Polymorphisms in drug metabolizing enzymes, drug targets, and disease pathogenesis genes are associated with therapeutic effect to cardiovascular pharmacotherapy. Moreover, pharmacogenomics and functional genomics are expected to have a profound impact on the process of drug discovery and development. Finally, pharmacogenomics is likely to transform the way clinical trials are conducted by allowing for the selection of a more homogeneous study population, thereby reducing the size and cost of clinical investigation.