Stark had the arc reactor in his chest removed after receiving surgery to remove the shrapnel from his chest. He later removed the element and then threw the decommissioned unit into the ocean. Stark soon returned to building arc reactor technology and used a number of them to power later generations of Iron Man.
Following the Avengers' mobilization in order to partake in the War on HYDRA, Tony Stark created Iron Man armors that had built-in Arc Reactors in them, as he no longer required one in his chest.
He was able to survive without it because the surgery he underwent at the end of Iron Man had removed the shrapnel from his heart, making the arc reactor no longer necessary to keep him alive. In the movie, it is shown that Tony has a scar on his chest from the surgery.
Does Tony still have the arc reactor in Age of Ultron?
Did Stark have the arc reactor in his chest in Age of Ultron? No, Tony Stark did not have the Arc Reactor in his change is The Avengers: Age of Ultron. At the end of Iron Man 3, Tony gathered enough courage to have the shrapnel removed from his chest.
In the finale of Iron Man 3, Tony Stark undergoes surgery to remove the shrapnel in his heart which meant that he no longer needed the arc reactor attached to his chest.
Tony Stark also used it originally for his miniaturized arc reactor, but when it began to poison and slowly kill him, he replaced it with a new element he managed to synthesize using his father's old notes.
He recreated the element by using a Particle Accelerator in his basement and created a brand new Arc Reactor to utilize the new core and a new suit that could better utilize the higher energy output, as well as cure him of the palladium poisoning in his blood.
When it was suggested early on in Tony Stark's time in the MCU that he get surgery to remove the shrapnel from his chest, he was decidedly against this. He found out that he would pretty much instantly die if such surgery were performed. Because of how the shrapnel had entered his body, it was impossible to remove.
The only reason that it isn't removed before it happens is for story complication and cause the writers didn't want it to be. That said there is probably internal psychological reason as to why he doesn't get it done sooner.
The arc reactor keeps Tony Stark alive. In the different versions of Iron Man, Stark's group has been ambushed in Vietnam, the Persian Gulf, and Afghanistan. Stark sustained serious injuries as a result. He created the personal arc reactor to generate energy for an electromagnet keeping shrapnel away from his heart.
Fury provided Stark with some of his father's old things. He discovered an element that could fulfill his needs through a hidden message. He proceeded to re-create this new element (using the molecular structure provided by his father) and created another arc reactor that cured his palladium poisoning.
A far more feasible method of survival—and another one that stems from the comics—involves Tony's own inventions. Tony could have invented an AI version of himself that would have survived his physical death. This actually happens in the comics, and AI Tony acts as the assistant for his protege, Riri Williams.
Taking inspiration from his Mark XLVI armor, Tony Stark created the Iron Spider Armor that contained many new features over the previous suit such as a collapsible helmet and incorporating miniature arc reactors.
In the Iron Man 2 novelization, the new element created by Tony Stark to replace Palladium in the arc reactor is called Vibranium. This information would later be invalidated by Captain America: The First Avenger, where Vibranium is shown as a rare metal already existing in the 1940s.
The concept of the arc reactor doesn't work in real life because it violates the Law of Conservation of Energy. Energy can't be created or destroyed, only transferred. The arc reactors in the MCU are essentially perpetual motion machines, which don't work. Instead, this arc reactor is powered by a 3.7V LiPo battery.
Why did Thanos spare Iron Man an Infinity War? Well, of course, it's because he made a bargain with Doctor Strange. But Thanos had every opportunity to break that deal. and kill him after getting the stone, which would have stopped them from defeating him in.
In the former movie, it was likely Tony's narcissism and lack of humility that contributed to his “unworthiness.” These attributes did, however, make him a hero. After saving the world, making a play to sacrifice himself, and defeating Thanos' army, he was not able to lift Mjolnir in Age of Ultron.
Tony Stark's personal journey in the MCU led him to destroy his Iron Man armors as a way to prioritize his relationship with Pepper Potts. Although Tony initially retired and destroyed his armors, his relentless commitment to improvement and his obsession with being a hero led him back into action.
Tony didn't meet him on the roof that night in Switzerland to talk about his AIM project. He didn't seem interested and he was more into the work Maya was working on. That was his reason for his hatred of Tony Stark, but overall, he was evil because of his controlling improvements of the human body.
[1] Despite the many physical dangers that Tony faces as Iron Man, I argue that his greatest foe will always be self-doubts and sense of his own inadequacies. These doubts and supposed failures are amplified by Tony's post-traumatic stress disorder (PTSD).
Given this progression, he never got the chance to build a suit that's made from one of the strongest metals on Earth — Vibranium. Using the indestructible element seemed to be an organic next step for the Iron Man suit on the heels of Wakanda's opening under King T'Challa's rule in Black Panther.
More crucially, he says that his father King T'Chanda had gifted Howard Stark some Vibranium to help the war effort in the 1940s. In other words, Captain America's shield was made from Vibranium the secretive African nation freely gave to the Americans. Howard Stark: Your Highness, it's a pleasure.
