The heart's venous drainage system has been the object of observations and research for several centuries. Its anatomic and histological characteristics, as well as its distribution and architecture, make the cardiac venous system a uniquely organized structure within the organism. An understanding of its physiology helps in comprehending some of the mechanisms by which, under special conditions, the myocardium tolerates ischemia. The heart's venous system has become important today as a route for administering pharmacologic therapy, gene therapy, growth factors, and stem cells to the myocardium. Access through the coronary sinus is a common practice in modern electrophysiology.