Thomas Lewis was a British cardiologist who pioneered using science within biomedical practice during the 20th century. He studied medicine at University College in Cardiff in 1898, and became interested in physiology.

In 1902, Lewis entered University College Hospital, London, where he began investigating the pulse and blood pressure. In 1908 he met James Mackenzie, an important heart doctor. Mackenzie convinced Lewis to study irregular actions of the heartbeat, but Lewis realised that to do this he needed an electrocardiograph, a visual trace of the heart’s electrical activity. Lewis published his research on the mechanism and disorders of the heartbeat in 1911. He was responsible for electrocardiograph machines being accepted by hospital doctors.

Lewis worked at the Military Heart Hospital in London during the First World War, where he studied the condition known as ‘soldier’s heart’. Lewis showed it was not a cardiac condition, but a response to overexertion. He named it the ‘effort syndrome’. Like shell shock, it appeared to be related to the trauma of war. It has since been suggested the condition may have been psychiatric rather than physiological. Lewis devised special exercises to help soldiers return to duty. He spent his career researching skin reactions and pain mechanisms. Lewis was passionate about applying science to problems doctors encountered. He founded the Medical Research Society in 1930 to help young researchers.

Lewis died of a heart attack in 1945.