While working at the Bellevue hospital in New York, he was awarded a fellowship to London to continue his studies in medicine.
During the Second World War, Harken served in the U.S. Army Medical Corps in London as a surgeon and had previously operated alongside Tudor Edwards.
[2] In 1948, Harken discovered a way similar to how he operated on soldiers to correct mitral stenosis.
At first, the majority of patients died, however as the method was refined, the fatality rate dropped and became safe.
Harken's concept of intensive care has been adopted worldwide and has improved the chance of survival for patients.