[1][2] In 1779 Pitcairn began practice in London, and was elected a fellow of the Royal College of Physicians on 15 Aug. 1785.

John Latham mentioned, in his treatise on gout and rheumatism, that David Pitcairn was the first to discover that valvular disease of the heart was a frequent result of rheumatic fever, and that he made his discovery known in his teaching at St. Bartholomew's Hospital.

[2] Pitcairn had frequent attacks of quinsy, and failing health, accompanied by hæmoptysis, in 1798, forced him to give up work and spend eighteen months in Portugal.

Matthew Baillie, a close friend for 30 years, attended him, and described his case, with the similar one of John Macnamara Hayes, who died of the same disease three months later.

Pitcairn's body was examined by Benjamin Collins Brodie the elder, in the presence of Baillie, Everard Home, and William Charles Wells.