Carl Wilhelm Hermann Nothnagel (September 28, 1841 - July 7, 1905, Vienna) was a German internist born in Alt-Lietzegöricke (Polish: Stare Łysogórki), nearby Bärwalde in der Neumark (Polish: Mieszkowice), Neumark, Brandenburg.
Son of a pharmacist, from 1858 to 1863 Nothnagel studied under Ludwig Traube (1818–1876) and Rudolf Virchow (1821–1902) at the University of Berlin. From 1865 to 1868 he was an assistant to Ernst Viktor von Leyden (1832-1910) at the University of Königsberg, where he in 1866 he was habilitated for internal medicine . From 1868 to 1870 he worked as a military physician and lecturer in Berlin and later served in the same roles at Breslau (1870-72).
In 1872 he relocated to Freiburg and in 1874 was appointed full professor at the medical clinic in Jena. From 1882 until his death in 1905, he was a professor at the university clinic in Vienna. One of his better known students was Constantin von Economo (1876-1931). In 1879 he became a member of the Deutsche Akademie der Naturforscher Leopoldina. He is interred at the Protestant Friedhof Matzleinsdorf (top middle vault, No. 109).
In collaboration with other physicians, Nothnagel published Handbuch der speciellen Pathologie und Therapie, a comprehensive 24-volume handbook of medicine. In 1876 he described the irregular pulse associated with atrial fibrillation. At the time he referred to this discovery as "delirium cordis". The eponymous "Nothnagel's syndrome" is named after him.