The human heart, as Castiel knows it, is a hollow muscle, located anterior to the vertebral column and posterior to the sternum. It is the size of a closed fist, and, during the average human's lifetime, it will beat approximately 2.5 billion times.

He knows that the heart has four chambers. He knows that deoxygenated blood flows into the heart via the superior vena cava. He knows that, once oxygenated, it leaves via the aortic valve to the aorta. He understands the rate at which it does this, the electrical impulses that keep it going, pumping and pumping for decades.

He knows that it is fallible and vulnerable, subject to any number of diseases and injuries, and to look at, it isn't much more than a lump of wet, bloody meat.

These are all things he knows.

But as he sees it now, the heart is infinitely more than this.

The average human heart might weigh around 300 grams, but the weight of its memory is much, much greater.

To think of the heart as nothing but an organ, even one so integral to survival, suddenly seems obscene.

A gross understatement of its importance.

As he lands, quiet as a breath, he understands wholly that it is not merely a part of the body.

It is a part of the soul, and it becomes one with all the things it touches. All the memories it holds, all the hopes it protects, all the connections it forms.

The human heart is not an organ, but a light, a beacon that calls home those whom you have lost.

It's so clear, now.

He thinks all this in the space of time it takes for his wings to settle, and for the first time in months, he smiles.

Dean is asleep, and Castiel knows it's only through the heart's memory that he has managed to find him here, in this place hidden from the outside by countless sigils. For the first time in his existence, he had flown blind, following nothing but that feeling, that feeling that said I am here and I am waiting.

Now, Castiel lets his grace reach out, hovering over Dean's chest to feel the echo, pulsing with his blood. It steels him, grounds him, yet at the same time makes him feel so light that he might spin off into the sky. He watches the rise and fall of Dean's breath and wonders how he never felt this before. If it had been there and he had missed it somehow, or if it were something new, something that had blossomed in his absence like a forest sprung from lost grace.

He can still feel the distant pull of Naomi searching the halls of Heaven for him. But he is hidden here. She won't find him so long as he manages to stay. So long as he manages to remember her.

If he can remember, he will know not to respond to her call.

If he can remember, he will know not to allow himself to be dragged back into her chamber.

He should wake Dean, he knows. He should wake him and tell him now before he forgets, tell him that he doesn't have long, that he is being manipulated and twisted to the will of Heaven.

He knows all this, but cannot bring himself to disturb Dean's sleep. Not yet.

He wants instead to savor this moment, to feel the hearts memory that guided him here.

It has been a long time since he's seen Dean; even longer since he's seen him sleeping so soundly. He looks peaceful, and his dreams-though Castiel hasn't taken the liberty of looking at them-must be pleasant if the calm smile on his face is any indication. His breath is slow and steady. One arm is wrapped loosely around his pillow. Every now and then, a contented sigh slips from his throat and he hugs the pillow tighter.

No, Castiel thinks, not now.

So he waits, feels the hearts memory pulse, sees how it seems to reach out to him, listens to the way it settles against his grace and the room around him.

This room, he notices now, is not a place he has been before, and it is distinctly Dean. Not another nameless motel room, not an abandoned building or a comandeered bedroom in the house of some stranger. Somewhere nearby, in another room, he can hear Sam breathing. There's an overwhelming sense of home here, and somehow, though he can't quite understand how, a feeling of history, of blood and inheritance.

In this room, Dean's room, weapons adorn the walls. One blade stands out in particular. Oversized and hand made, stained black with the filth of Purgatory, it acts as a centerpiece, a focus. The sight of it is troubling in this place; this peaceful place that hums with the attachments already formed on its every corner. Castiel turns away from it, focusing instead on a photograph that sits on the desk. In this photograph, he feels the heart more than anywhere else, so much it almost glows. Castiel picks it up, feeling the smooth paper, the warmth of Dean echoed in its surface. Two smiles reach out from its surface, mother and son. So much heart, so much love.

It is a melancholy thing.

Briefly, he wonders how well Dean remembers her.

Despite the feeling that pours over everything in sight, the room is somewhat sparse. A side effect of having lived a life largely on the road means that Dean possesses very little in the way of material objects, and since setting up this new home-and Castiel knows, instinctively knows, that's definitely what this place is-he has made very few additions.

Curiously, though, there's a typewriter, and the buzz of energy that surrounds it tells him that it has been a point of intense focus for Dean over the last few days. There are a few scrunched up balls of paper in a wastebasket beside the desk, each thrumming a little, and a single sheet with curled up edges remains, rolled around the platen, waiting to be filled. A few words have already been tapped out in black ink, and on closer inspection, he sees that they have all been struck through with a series of heavy X's.

He touches a fingertip to the surface and it comes away black. Castiel frowns, wondering what Dean was writing about, and glances back at his prone form. He is still sound asleep. Castiel listens for a moment to the sound of his breath before turning back to the desk.

A turntable sits to one side, and beside it are a few vinyl albums. They give of a dusty, warm, homey kind of smell and Castiel inhales deeply, thinking he could quite easily get lost in a smell like that, especially when it is all woven together with an intense sort of reverence that until recently he could only have associated with the Host of Heaven.

Music, he thinks, might be the closest approximation of the tangible part of the soul that human beings will ever find. But perhaps, as a being made up largely of light and sound, his opinion on the matter is a little biased.

Regardless, he feels an affinity for recorded music, and he slips the closest record out of its white sleeve to study the waveforms in the vinyl.

After barely a moments hesitation, he presses his grace into the grooves and listens as the music merges with his being. A string section swells from nothing, and a soft baritone voice, velvet and soothing, melts into him. Castiel can feel the warmth in the soul captured by the record, can almost hear the calm smile on the singers face, and finds himself smiling in return. He sways with the song, feels a little like he is the song in this moment. He shares his body with it, lets it become a part of him, and feels so much that he forgets himself. He is so absorbed in the music, he doesn't hear the sudden intake of breath behind him. Doesn't notice that Dean is awake until he is standing directly behind him, his fingers on Castiel's elbow, voice low and worried.

"Cas?"

Startled, he turns, the song still moving within him. When his eyes meet Dean's he feels the hearts memory flare for a moment, brighter than ever, before being drawn back in, almost forcefully. Dean's face is stony, but in his eyes there's a little of that light left.

"Hello, Dean."

"Are you okay?"

"I'm fine."

Dean eyes him for a moment before he shakes his head and takes a step back.

"You weren't answering."

"I didn't notice you were awake."

"No, I mean... it's been months, Cas. Almost three months."

He sinks down onto his bed, rubbing both hands through his sleep-mussed hair and avoiding eye contact.

"I wanted to come sooner. I tried."

"Where were you?"

"In Heaven. They were... holding me, I suppose, is the best way to put it."

The hearts memory burns bright in Dean now, a power surge, bursting from him in fiercely protective anger, and he is on his feet.

"They? They who? Did they hurt you?"

"I'm okay now."

"What did they do to you? Last time I saw you, Cas you didn't look right. What's been-"

"I'm here now. They can't reach me now."

Castiel feels the hearts memory being pulled in tight again, and he frowns.

"Why do you keep doing that?"

"What?"

"Trying not to feel."

For a brief moment, Dean's eyes go wide, and Castiel steps closer, looking at him as though he might see the reason written on his face. Dean shakes his head minutely.

"Do you think I don't-"

"Don't, Cas."

"What?"

"I can't... I can't have this conversation right now."

He sits back down, limbs stiff and fists clenching, and Castiel watches him as he struggles to reign in a feeling he barely understands.

That's when it hits him.

The human heart is not an organ, but a photograph, creased and faded by time and fingerprints. It is a song felt deeply. It is a book, dog-eared and worn down at the spine, stained with spilled coffee and blood from one too many paper cuts. It is a room in which to sleep in peace.

The human heart is not an organ, but a willingness to give oneself over entirely for the sake of another. It is hope and it is pain and it is everything that makes either worth all the inevitable trouble they bring.

It is everything, and for someone who has made do with nothing for the majority of his life, it is too much. Fear of loss is only natural. Castiel feels his grace ache in sympathy, in longing.

"Dean."

Dean presses his eyes closed, purses his lips together. A muscle in the side of his jaw twitches. He doesn't respond, not even when Castiel sits down beside him, making the mattress dip down. Just tenses, despite the fact that his hearts memory is ringing like a struck bell, humming deep in his bones and out to his fingers.

"Dean, just listen."

On instinct, Castiel reaches out and touches his fingers to Dean's wrist, circling it, and Dean's eyes flick open. The music, still flowing through Castiel, passes through their skin, from Castiels grace and into Dean's soul like oxygen, and as it goes on, as the swell of string and brass and lyric rises, Dean breathes. Breathes deep.

Presently, he turns his hand over, stares down at where Castiel's fingers are moving now, slow, over his pulse point.

"Okay," he says, finally, raising his eyes to meet Castiel's, "tell me."

With everything he has ever known, Castiel knows now that words are not enough, and he raises his free hand to feel the scratch of stubble, the smoothness of a lip beneath the pad of his thumb.

The song goes on, humming through them, joining them.

The heart is not an organ, he thinks, as space dissolves between them, it is this, just this.

And as it turns out, lips have a kind of memory, too.