Jean-Baptiste de Sénac (1693–1770) is believed to have studied medicine at the University of Leyden and in London. He began to practice medicine in Paris in 1723 and served as the personal physician to King Louis XV. He studied the heart in an era when cardiology was rudimentary. In 1749 he published a book on cardiology in which he described the relation between atrial fibrillation and mitral valve disease as well as between cardiac size and its “force,” attributing cardiac hypertrophy to valvular disease. His observations were derived from autopsies and he also studied the action of cinchona extract and rhubarb as possible treatments for cardiac irregularities.