Even though Tony Stark had his life-saving arc reactor removed in Iron Man 3, the McU's Iron Man still uses the technology during his later Marvel Studios appearances. After being taken captive by the Ten Rings in Iron Man, Stark equips himself with a miniaturized arc reactor, with the help of Ho Yinsen, which prevents pieces of metal shrapnel from making their way into Stark's heart. This technology would later become the power source for Stark's Iron Man armor in his initial MCU adventures, until Iron Man 3 saw the device become redundant after the shrapnel was surgically removed from Stark's body.

While Stark went without an arc reactor during Avengers: Age of Ultron, Captain America: Civil War, and Spider-Man: Homecoming, Avengers: Infinity War saw Stark sporting a very different arc reactor. Stark's first arc reactor had two purposes: to keep the shrapnel from entering his heart, and to power his suits,...