A/N: For horizon-labs, who asked for "a fic in which Steve is unconcious/dying and Tony takes the arc reactor out of his chest and gives it to him to save him. And then Steve's reaction when he wakes up." Here ya go. Hope it's what you were looking for! I split it into two chapters because I hate switching POV in the same chapter. I'm so sorry about the questionable science.

They've been stuck in the cave for over twelve hours and Steve isn't getting any better. His wound is still bleeding sluggishly and he stopped responding to Tony's endless stream of questions a little over an hour ago. Tony's trying not to panic, but he's never liked caves, even before Afghanistan. He likes them even less now. And there's the small issue of his teammate lying semi-conscious on the cold, damp cave floor, but Tony's trying not to dwell too hard on that. He's already gotten out of his now-useless suit, and has torn up his undershirt and part of Steve's armor to use as bandages, but he's starting to run out of clean material and Steve's still bleeding.

It's been over twelve hours and Steve's still bleeding. The serum's helped – a normal man wouldn't have survived that blast from Ultron – but his skin is flushed and his breathing is shallow. The other Avengers have to get them out eventually, but Tony morbidly wonders if they'll get there in time. The cave's mouth is filled with rocks and debris, and Tony's suit is too damaged to blast their way through.

Steve's skin begins to lose its sheen after another hour and the bleeding begins to slow down bit by bit. Tony's relieved until he sees Steve's face begin to turn ashen. He reaches over and shoves his fingers against Steve's throat and he instantly feels his stomach bottom out. Steve's pulse is almost non-existent. Tony quickly begins doing chest-compressions, those damn CPR lessons that he learned in boarding school all those years ago coming back to him, the instructor's annoying voice chirping in his head. He counts steadily and breathes into Steve's mouth. He wishes things were less dire so he could make a joke about kissing, to taunt Steve's blushing face and throw his arm around Steve's broad shoulders, but the only thought in Tony's brain is a desperate plea for his friend to live. They've only been teammates for a year and friends for a little less, and it's not enough. It's nowhere near enough because Tony wants everything.

He finally stops the CPR when Steve's pulse begins to strengthen again, and he lets himself fall back on his ass. Nausea coils tightly in Tony's gut, and he has to take several deep breathes to keep himself from throwing up. The air is dank and it crowds Tony's senses, pulling him down, down, down into an overwhelming swirl of dizziness and claustrophobia. And suddenly, it's all too much – the painful memories of his captivity in Afghanistan looming over him, bittersweet memories of fighting with Steve, laughing with Steve, arguing with Steve, the biting fear that Steve might not make it out of this cave alive. It's too damn much for Tony.

He breathes for several more moments before wiping the sweat and dirt from his eyes and turning back to Steve. Steve, who's the bravest man he's ever known. Steve, who's so good and earnest and believes in people so much. Steve, who makes everyone better just by being around him, even hopeless cases like Tony Stark. But even someone as hopeless and messed up as Tony can't let Steve Rogers die. If he managed to build his first suit from a box of scraps, he can damn well find a way to save his best friend.

Re-energized, Tony pulls himself to his feet and starts disassembling his ruined suit. He makes quick calculations in his head and scratches the more complex ones on the dirt floor, his arc reactor serving as the sole light source. His equipment consists entirely of scraps of his armor and torn off chunks of Steve's armor. He works diligently and stubbornly ignores him throbbing ribs.

It takes him longer than he would have liked - he's had to stop twice to give Steve CPR again– but he finally manages to come up with something semi-usable. The chest compressions can only do so much and the pressure causes Steve's wound to start bleeding again, but the little device he's cobbled together should be able to give Steve's heart enough juice to keep beating, at least until the others get them out. The only problem is that the only power source available is Tony's arc reactor. He lost track of time while working, so he has no idea how long they've been stuck in that cave. The rest of the Avengers could be moments away from getting them out or they could be hours away. If Tony takes his arc reactor out, if he gives it to Steve, he'll only have a few minutes before the shrapnel tears into his heart. He knows he's going to die, that he's never going to see Steve or the rest of his teammates ever again. He'll never see Pepper smile fondly at him or yell at him for missing another meeting. He'll never get to punch Thor's smug little brother's face like he promised to do the last time Loki tried to take over Earth. He'll never see Steve laugh or hear his serious, Captain-y voice giving out orders over the comms. He'll never order pizza from that place on 7th and watch Steve inhale two whole pies while watching stupid movies. He'll never get to puzzle out what exactly Steve means to him.

Tony doesn't hesitate to pull the arc reactor from chest. What other choice does he have? It was never a question because how could he not give Steve a fighting chance? A world with Tony Stark is fine, but a world with Captain America, without Steve Rogers, is a world without hope.

Tony carefully unwinds Steve's bandages and deftly connects his reactor to the makeshift pacemaker. Wires are crossed and rearranged until the crude device is finally in place. It glows brighter in Steve's chest than it ever did in Tony's. Steve finally begins to breathe easier, and his pulse steadies. Tony, gasping, shivering and pale, smiles tiredly at the sight. He doesn't think he's seen anything more beautiful than Steve's face lit up by the glow of the arc reactor. It had always looked hideous to him, but Steve makes it beautiful. He makes everything better.

Exhausted, Tony collapses next to Steve. He takes Steve's hand and holds it in his as his body begins to slow down. He bizarrely wonders what Steve thinks about sofas before he starts to see black spots dancing in front of his eye. Steve's hand slips from his own clammy one right before the black spots multiply and everything simply stops.

A/N: The "Steve makes everyone better just by being around him" is paraphrased from one of Clint's lines in Hawkeye (2012) #1. The actual line from the comic is "…having Captain America around you all the time. He just – the guy brings out the absolute best in people." Part two will be up in a little while.