MB Cm Edin 1878, MD 1882, LLD 1911; FRCP 1913.
Mackenzie was born in Scone, Perthshire on 12 April 1853, and forged a reputation as a distinguished cardiologist. After studying medicine in Edinburgh and a period of residence at MRI Mackenzie settled in general practice in Burnley, Lancashire in 1879 and was appointed physician to the Victoria Hospital. While at Burnley he began extensive clinical studies, for which he became known. Mackenzie moved to London in 1907 and in 1913 became consulting physician to the London Hospital. He gained many honours during this period, being elected a fellow of the Royal Society and being awarded a knighthood in 1915. Mackenzie made a number of discoveries while engaged in heavy industrial practice. He wrote on the interpretation of symptoms and on angina pectoris. Mackenzie was best known for his researches on irregularities of the heart's rhythm, he made the first simultaneous records of the arterial and venal pulse to establish the clinical function of the heart. Mackenzie died from angina pectoris on 26 January 1925.