The Stark Heat Vest was Howard Stark's prototype for a new armor system intended to double as a heat-source for use during the winter months on the Western Front.
In his efforts to create a new, improved body armor system for troops fighting on the Western Front, Howard Stark created a prototype Heat Vest. As the name implies, the armor was intended to double as a heat source, which could be used during the winter months. If a soldier locked the armor, it would activate a battery, powering the internal heating mechanism.
Because the energy source used for the prototype was incredibly flawed and would invariably overheat with explosive results, the prototype never saw production. It was stored in the vault under Howard Stark's Mansion.
Peggy Carter and Edwin Jarvis found Howard Stark's missing inventions, which were stolen from the vault in his mansion by former Leviathan agent Leet Brannis. Carter and Jarvis located the stolen property on board The Heartbreak. Jarvis called the New York Bell Company branch of the Strategic Scientific Reserve; and a team of agents was sent to retrieve the items. The prototype of the Stark Heat Vest was among the recaptured inventions.
Ivchenko, searching for Item 17, found the Heat Vest among the other inventions that were confiscated from The Heartbreak. As he lifted it, he remembered the stories about this invention. Ivchenko warned Roger Dooley to be careful while handling it.
The two walked to the elevator and Ivchenko traded the Heat Vest he was carrying for the container holding Item 17 that Dooley had. As Dooley began to wake from the thrall of Ivchenko, the doctor used his power on Dooley once more to keep him under his control.
Dooley awoke from his dream to find himself wearing the activated vest and surrounded by Strategic Scientific Reserve agents. Though the agents sought to remove the Vest, Edwin Jarvis advised them not to or it would explode. Peggy Carter went to ask Alex Doobin for suggestions on what to do. Unfortunately, Doobin told the agents that he did not know how to help.
Out of options, Dooley grabbed a gun from Jack Thompson and had Carter promise that she would bring Ivchenko to justice. He then began firing at a nearby window as he ran towards it, jumping through to save the others from the impending detonation.
The Stark Heat Vest is made out of a special alloy, making it resistant to temperature extremes and artillery blasts. It is powered by an internal battery, which was powerful, though experimental and extremely flawed. Locking the armor ignites the power source, which will invariably overheat until the vest explodes.