I'm no anatomist (if that's a word), but, with the space required for the arc reactor, not only would you be out a large part (90%) of your sternum, but you'd also lose your heart, and parts of (if not all) of your stomach, lungs, esophagus, and trachea.
In reality, for the reactor to do it's proper function, you think it'd need to be outside the chest, not IN the chest. War Machine wears the suit just fine without a huge piece of machinery in his chest
You'd think, if the point of the reactor is to keep shrapnel out of his heart, that when returning to the states - if present doctors and tech can't save his heart, with his billions he could get a transplant or something.
Exactly. No one would EVER go to this elaborate length to basically implant a fancy self-powered electromagnet in your chest. First of all, you would never survive the oiperation, even in the best of crcumstances. A Cardiothoracic surgeon would REMOVE THE SHRAPNEL and repair the heart directly - if too much damage was done, they would transplant a donor heart.
Some biology here (yes, I've been in numerous heart operations):
If the shrapnel was in you cardiac muscle, BUT YOU WERE STILL ALIVE, then there is no tamponade. The heart sits in a "sac" of fluid called the pericardium. When injured, you can bleed into this sac and strangle the heart, as there is no way for the sac to decompress. This is a "tamponade" situation.
Tony was still alive after the fancy magnet was stuck in his chest - therefore, any tamponade present from the shrapnel was minor, OR the extra "sac of blood" was drained when the magnet was installed.
Shrapnel in the heart, if deep enough, would tear all the way INTO the atria or ventricles, and your heart would most likely bleed out. You would die, quickly.
Shrapnel in the OUTER muscle layer of the heart may NOT immmediately damage the heart, at least not severely enough to cause near instant death. HOWEVER, all of the shrapnel would have had to "dodge" the coronary arteries, which sit on the outer surface of the heart - otherwise, instant heart attack. A piece or 2 might not hit anything serious - but MULTIPLE pieces of metal fragments from a concussive explosion, into your heart?! Not a chance you would live.
When penetrating the chest, unless it was DIRECTLY OVER THE STERNUM, shrapnel would have to hit the lung(s) on its way to the heart. Tony would have had at LEAST one collapsed lung, which he could have survived, but he would have never made it with two collapsed lungs. No breathing = you're dead.
So yeah, it's pure fantasy. Couldn't happen in even the BEST of circumstances. Tony's chest must be the Tardis or something, to have that much room in there!
...unless you're John Connor, then you CAN have a heart transplant performed, outside, in the middle of the desert, with no anti-rejection medication, from an incompatible cyborg donor, and you will live.