The cardiac side effects of chinchona bark were discovered very soon after its introduction to the materia medica of academic medicine towards the end of the 17th century (Georg Ernst Stahl, 1660-1734). Therapeutically these effects were utilized sporadically as early as in the first half of the 18th century (Gerhard van Swieten, 1700-1772; John Wall, 1708-1776; William Saunders, 1743-1817). Purified quinine became a standard component of cardiac therapy in the 2nd half of the 19th century (Ludwig Traube, 1818-1876; Johann Oppolzer, 1808-1871; Karel Frederik Wenckebach, 1864-1940). In 1918 quinidine was introduced by Walter Frey (1884-1972) as the common alkaloid of chinchona bark and is still used in rhythmology today.