Who performed the first open heart surgery?

Not enough info. Open heart surgery may simply refer to an exposed heart in the chest. The surgery itself may be as simple as a biopsy or as complicated as a vessel bypass with valve replacement and aneurysm repair. You may also be referring to the use of cardiopulmonary bypass which allows surgeons to stop the heart and essentially pumps blood to the other vital organs while the heart is repaired.
References vary. Daniel hale williams is reported to have performed the first successful open heart surgery in america in chicago in 1893.