Open chest cardiac procedures were done without any anaesthesia or pain relief during this period because it was believed the baby didn't experience any pain. The turning point really came from the observations of a petiatric anaesthesiologist, who noted that during these open chest cardiac procedures  the heart rate went up dramatically. He began also measuring other markes of stress hormons and showed that indeed, there were these dramatic rises in stress hormones,. indicating the baby indeed was experiencing distress. This was in the late seventies, early eighties, and i hate to say that that evolution of knowledge and understanding is still in progress. But one thing have learned is that, in some ways, the pain these