In 1983 he returned to his native New York, spending six years at the Albert Einstein College of Medicine, in the Bronx, specialising in anaesthesiology.

In 1989 Hartstein returned to Belgium and began working at Circuit de Spa-Francorchamps as part of the local medical team attending races.

In 1990 Hartstein was assigned to the medical car containing Professor Sid Watkins and the two physicians immediately formed a firm friendship.

Hartstein's work at the Belgian Grand Prix continued until 1997 when the FIA, realising the need for an anaesthetist to assist Watkins, recruited him.

He was also, with Prof Gerard Saillant, behind the creation of the "FIA Institute Faculty" (FIMF), which will seek to consolidate the expertise of motor sport doctors and medical staff around the world, on the model of professional associations.