Bruce: My heart! Pounding — straining! Keep cool, Banner! For Jen’s sake — Keep cool! Across the street — a doctor’s shingle! No answer! Not a sound inside! There’s — nobody home! But I can’t fail her now! I can’t! I can’t!!She’s weakening! Can’t wait any longer! I’ll do the transfusion — myself! I’ll give her my own blood!
( The Savage She-Hulk #1 — Stan Lee & John Buscema )
in case you’re new to the She-Hulk origin story, while working on a case against Trask, she gets shot by some mafia members. with Jen dying in his arms and Bruce being the only person around at the time, he does the only thing he can do in his situation — try and save her life.
(the fact that Jennifer pointed out that he was in med school at one point the panel before this, now proves to be pretty important.)
he decides to give her a blood transfusion, and what is important about this is, as we all know, Bruce is the Hulk. so his blood is a little gamma-radiated. a little.