When and why did Tony Stark dig a hole in his chest?

In the beginning of the first movie he is shown in the cave with some wires hanging off his chest attached to a battery of sorts to keep the shrapnel out of his heart.

Later after he invents the smaller circular battery thing he asks Pepper to replace it and suddenly he has a substantial hole in his chest instead of a superficial battery like he had in the cave.

Was there something in the comics or unexplained in the movies to justify or explain the seemingly unnessecary gaping hole in his chest?

marvel-cinematic-universe iron-man

Best Answer

The initial device fitted to Tony is already implanted within his chest cavity...

And the initial accompanying power source (the one the device was designed to draw from) is anything but superficial...

The job performed by Dr Yinsen is effectively surgical triage; a short term fix to keep tony alive. What we see in the first picture is merely the exposed connections, the visible 'tip' of the iceberg. Yinsen had no idea Tony would wake up and develop the arc reactor, and will not have designed the electromagnet with that in mind.

The mini arc reactor Tony creates is another 'rush job' necessitated by circumstance rather than careful planning; albeit truly the mind of a genius is able to improvise such a technology. To be blunt; the original device in his chest was a short term measure, and as such needed a short term power supply.

We can see from the first photo that the flesh around the wound is looking as though it is turning septic. We see Tony remove the power source and replace it later in the movie, with the assistance of Pepper.

He is clearly in a surgical environment, and the wound and necrotic flesh have been replaced by a metallic container for the power source. It stands to reason that to house the new power source (safely and effectively), Tony was required to modify the area of his chest that had the 'emergency' procedure applied. If this means expanding the affected area, that's a necessary part of the process.