Robert Downey Jr as Tony Stark in Iron Man working on his Iron Man glove with the reactor


Iron Man's Nastiest Armor Detail Still Makes No Sense
Tony Stark/Iron Man has been around since 1963's "Tales of Suspense" #39, but the idea of his life-saving power source being embedded in his chest is a fairly recent one.
In his comic book debut, Stark's suit prevents shrapnel from piercing his heart. The core piece of his original suit is an electromagnetic chest plate that he must always wear.
This chest plate is completely external in the comics, which means that Tony’s chest cavity in the early MCU movies was never originally part of his character.
While Pepper gives Tony his original arc reactor as proof of him having a heart at the end of "Iron Man," it’s hard to tell where his heart is within his body after his accident.