Lets remember the names...
Vivian Thomas was an employee (surgical research technician) of Vanderbilt University (as I recall) who was assigned to assist in Dr. Alfred Blalock in his lab. Blalock brought Thomas with him to Hopkins when he assumed positions chief surgeon at Hopkins and a professor and director of the surgical department in the medical school. There, they worked out how to run a shunt to pass blood from the lungs to the heart which improved oxygenation and was a fairly successful treatment for what they called "blue baby syndrome."
Dr. Taussig, another doctor working on the problem, shares credit for the procedure with Blalock. Thomas perfected the operation on dogs, first working out a way to recreate the congenital defect, then a way to correct it. He also devised a number of specialized surgical instruments needed for the procedure and served as a guide for Blalock who (when they first started out) had only very limited experience with it.
Recognition for Thomas' efforts came very late mostly due to segregation and racism (the world in which they lived) in the post-WWII era... Hopkins was essentially "whites only" as far as medical students went and Thomas was denied the opportunities to become a surgeon.
He did teach at Hopkins though and was eventually awarded an honorary degree in law, there are regulations that prohibit honorary degrees in medicine.