"Class" was introduced by Servitus Tullius in the second century AD to designate the six categories into which the Romans had been divided for purposes of taxation. The term has since dissociated itself from taxes, but like taxes (and death), classification became one of life's eternal certitudes. Everybody and everything is classifiable.
Although inescapable, classifications are not immutable. They change, adapting to changing concepts and newly acquired insights. Old criteria are discarded to be replaced by new ones that are better suited to available knowledge and altering needs. Such a change in criteria has been recently effected by the American Heart Association in the seventh edition of the Nomenclature and Criteria for Diagnosis of Diseases of the Heart and Great Vessels, written by the Criteria Committee of the New York Heart Association.
Unlike the old Functional and Therapeutic classification, the new Cardiac Status and Prognosis classification is based not on