John Marshall Cowan (1870-1947) descended from a long line of Glasgow medical practitioners. He was at the forefront in the great advances made in cardiology during the first quarter of the 20th century. He was a founder member of the Cardiac Club and the principal author of a major text book Diseases of the Heart, first published in 1914. He had a distinguished military career and was physician in charge of wards in the Royal Infirmary, Glasgow and Professor of Medicine at Anderson's College, Glasgow. This article outlines Cowan's life, career and publications and also provides an examination of his magnum opus, Diseases of the Heart.
Keywords: Cardiac Club; Glasgow Royal Infirmary; John Marshall Cowan; cardiology.