I worked on baby hearts too. Those were really tough, sometimes the heart was the size of a walnut. Or we'd have adhesions from previous stages, like Norwood, Glenn, & Fontan. Kids can't take a joke either - getting them off bypass could get dicey. I've sent more than one to PICU on ECMO. The Thoracoabdominal Aortic Aneurysm I described was the biggest case I was ever involved in. But right before I started in the OR, our team had separated co-joined twins. I would say that was probably the MOAS in my book. They did several 'practice' runs with the whole team and it was massive. Both twins initially survived, though I believe one died a year or two after.