At the start, he protests. Vehemently—or as vehemently as one is able to protest while flat on one's back, sweating and delirious and dangerously feverish.
"Don't want one. Never wanted one," he grits out during one of his more lucid moments that first night. "I. Don't. Want. One."
"I don't give a bleeding fuck what you want!" hisses John, ignoring the scandalised look from the nurse. "You lost the right to demand to get what you want the minute you decided to meet that madman alone, without thinking of what—" John's mouth shuts with a click of teeth and his fingers clench at his sides. He looks away, inhaling deeply. "You need one, Sherlock. You need a heart."
There is an answering throb, faint and aching, from the mass of slow-burning cinders behind his ribcage. Even faint as it is, it still adds to the agonising fire against his nerves, against his soul, enough that he chokes on a scream and tries to curl in on himself.
"No," he manages to sob, just as he feels himself slipping away into delirium. "No, no, no."
"Sherlock. You need one," John says wearily on the third day.
"I don't," he replies emotionlessly. He is worn to the bone. "People survive without them."
"Not always," the doctor murmurs, and turns away. "Not for long."
On the fourth day, he kicks Mycroft out of his room, flinging the folder (full of intelligence studies and emotion surveys and suicide rates in the heartless) at the door after him.
The stretch of the unhealed vertical incision up his chest makes him gasp in pain, but he rather thinks it's worth it.
The fifth day, the convulsions stop, but everything begins to go dull.
Sometime during the fifth night, the tiny embers of what's left of his heart begin to panic. Everything feels grey and detached and removed and not right.
Being heartless is not an advantage, the smouldering embers tell him. Swallow your pride.
But it's too late, and he knows it.
Nothing happens on the sixth day except that his brain replays the poolside meeting over and over again.
In his mind's eye, he sees the hand splayed over his breast, sees the panicked look on John's face, sees the gleeful smile on Moriarty's, sees the gun in his hand pressed to the other man's forehead.
I will burn the heart out of you, Moriarty whispers harshly, cruelly, lovingly, and does it, making good on his words even as the bullet rips through his skull.
Even a child can live without a heart. No one can live without a brain, Sherlock thinks.
The thought doesn't bring as much triumph as it should.
The seventh day—the last day, the day his heart will fully die—is when John storms into his room, looking exhausted and haggard but determined. He stands at Sherlock's bedside and places the heart in Sherlock's lap.
"I don't care what I have to do, or if you hate me for it," he says quietly, fiercely, intensely. "That," he points to the heart, "is going inside you."
The words come as if from a distance, but Sherlock comprehends the gist of it. He looks down at the thing in his lap.
The heart is gold and quartz, as artificial hearts usually are, but there is something different about it. Something beautiful, even to Sherlock's dulled, detached senses. Something special in the delicate etching on the chambers, perhaps, or in the strong moulding of the aorta. He runs his fingers over the ventricles, traces the atria, caresses the arteries and veins, moves the gears and catches and mechanisms not found on organic hearts.
His eyes move up to John's.
"You made this." Not a question; there is something very him about it.
The man at his bedside draws a shaky breath. "I did." He shifts from one foot to the other. "Not the first heart I've done, of course. There are a few of mine still running around in Afghanistan, or so Murray claims. Quality's—very good. Best materials. Please, Sherlock. Don't make this—"
"It feels different."
"...Yes." John clears his throat. "I suppose it would."
It doesn't make sense, not really, not anymore, but Sherlock gives a slow, sage nod anyway. He lays back in the bed, hands the heart to John, and says, "All right."
There is a beat of silence.
"All right? You—That's it?"
"Yes," Sherlock replies. The very last two sparks behind his ribs flare hopefully.
"O—oh. Right. Okay. I'll just. Get the nurse, th—"
"No," the detective protests, his hand snaking out to catch his flatmate's wrist. "No. I want you to do it."
John gapes at him. "But I'm not—"
"That's the only way I'll take it. If you do it."
The doctor swallows a bit convulsively, but comes back to his friend's bedside, the heart still cradled in his hand. "You're sure."
"Oh." It's barely a whisper. "All right. I—Now?"
"Now." Sherlock is already pulling off the hospital gown, clumsily taking his arms out of the sleeves and baring his chest, exposing the red, jagged incision where the skin won't knit together without a heart.
"You'll need something to collect the ash," he instructs blandly, allowing his eyes to drift closed.
"I'm a doctor. I know," John mutters. "This will hurt, Sherlock. You realise that, don't you?"
A shadow of a ghost of irritation spasms in the last embers of Sherlock's heart.
"Shut up and give me the heart," he snaps back faintly.
So John does.
There is only one thing more painful than having one's heart burnt out of one's chest: scraping the dead cinders out and replacing them with a new heart. There is no anaesthetic in the world that can ease either pain, and that is why transplants are so very, very rare.
So Sherlock screams and cries and shivers and convulses around John's hand in his chest cavity, struggling against the doctors and nurses helping to hold him down, while John soldiers on bravely, grimly, his hands red and slippery, working at attaching veins and vessels, organic to inorganic, long after Sherlock passes out with a wordless sigh.
On the eighth day, Sherlock wakes up to a slow thudding behind his ribs and a warm hand over his wrist, the fingers curled over his pulse twitching when he moves.
"Have you been doing that all night?" he slurs blearily, turning his head to look at John. "No need. There's an electrocardiogram machine right there."
"I know," John responds tiredly. "Go back to sleep."
"It's different from what I remember," Sherlock tells John the eleventh day after Moriarty burnt his heart out, when they have been back at Baker Street for all of thirty-six hours. He is curled up on the couch, motionlessly watching his flatmate try to write up a blog post.
"Different... as in uncomfortable?"
Sherlock thinks about it a moment. "No." Decidedly not uncomfortable. In fact, he has developed the disconcerting habit of placing his hand over his chest, just to feel the reassuring whirring and tapping and pulsing of the thing John constructed. "No, it feels... warmer. Not burning," he adds quickly. "Only warm."
"Ah," says John, wincing. "Makes sense."
"Does it? Why?"
John hesitates, his fingers hovering over the keyboard. "It doesn't matter."
And for once, Sherlock is too tired to bother prodding him.
The twelfth day is when he catches sight of the little glass bottle on a chain around John's neck.
There are ashes inside. His. The remains of his heart.
Sherlock looks away quickly, his hand creeping up to rub at the warmth in his chest.
"Oh," he breathes on the nineteenth day, cutting Bach off with a screech of unfinished notes and protesting strings. His chest pulls slightly, but the pain doesn't deter him in the least. "Oh. That's what it was."
John glances at him from over the top of his newspaper. "What now?"
"The heart. My heart. The heart you made for me."
"What about it?"
John is good at locking down his emotions, his expressions—he's a soldier, after all, to the very core of him—but Sherlock has known him for months, studied him for all that time, and so he catches the nearly imperceptible hitch in his voice.
Sherlock puts down the violin and takes three long strides to stand in front of John's armchair.
"Artificial hearts are made of gold and quartz," he recites, "for conductivity and regularity."
"Yes, I know. Was there a—"
"You put something else in mine."
"Yes." Sherlock leans down, places one hand on either arm rest. "You put love."
John stiffens. "Look, Sherlock, I—"
"It was unintentional, obviously." It is only an echo, a trace, not strong enough to directly affect his own emotions: clearly not part of some devious scheme to snare his affections. "You didn't realise it was there until it was finished, and then there was no time to make a new one. But I can feel it."
The doctor hisses out a breath. "I'm sorry. I didn't mean—"
"Is it, though?"
"Don't be dim," Sherlock replies, straightening up and marching back to his violin. "I just said it was."
The twentieth day is when John puts his hand over Sherlock's heart, takes a deep breath, and kisses him.
It is also the day when Sherlock folds his fingers over the bottle of ashes around John's neck, curves up the corners of his mouth, and kisses back.