Dr. Fleiszer completed both his undergraduate and graduate medical education at McGill University and is a member of the Royal College of Surgeons and a Fellow of the American College of Surgeons. In 2005 he was the recipient of the John Reudy Award for Innovation in Teaching, presented by the Association of Faculties of Medicine of Canada. That same year he was named to the Faculty Honour List for Educational Excellence within McGill University, in recognition of his contribution to teaching and support for educational leadership and innovation in the field of medical informatics. In 2011 Dr. Fleiszer received the MUHC Director General award in the physician category in recognition of his work in patient education. In 2014 he was recognized by the MUHC Department of Surgery and received the Outstanding Teacher Award.

He helped to establish the Montreal General Hospital Trauma Program and in that process became the President of the Trauma Association of Canada and Director of the Surgical Intensive Care Unit. He was the major force behind the conception and creation of the Cedars Breast Cancer Clinic and was the Director of that unit for many years. Currently his clinical activities are focused on the diagnosis and treatment of breast cancer.