Dean comes around slowly. The persistent ache behind his eyes makes itself known before anything else, followed shortly by the dull throbbing in his arm. It ebbs in time with his pulse, the Mark still asserting its presence, but now it's more discomfort than pain. He groans softly as he eases his eyes open. Above him, the lone lightbulb from earlier immediately makes him squint, and a turn of his head tells him he's back on the exam table.

The equipment carts are back upright, everything returned to its rightful place. There's an intermittent beeping coming from one of the monitors, and it takes him a couple of seconds longer to realize the EKG is switched on and its leads are attached to his chest. Blinking to try and clear his head, Dean tries to sit up, but immediately finds a resistance tugging at his wrists and ankles. He glances down at his body and then gives up. Looks like she did have to use the restraints after all.

"Hey."

The voice comes from close by his ear, and he twists his head round to look at the source. Grey eyes stare back. It seems Carter has pulled up the chair from by the door and is sat next to the table, elbow resting next his head and her chin propped up by her hand. She looks almost bored. "You done being all Psycho now?"

"I…" He begins speaking before his mind's truly caught up with the situation. "I'm so sorry…"

"I don't care," she cuts him off disinterestedly. "I just need to know if you're done with all that."

"I…think so." Dean can't be sure. He blinks again, taking another glance down at himself, and realising with a dull note of panic that his belt is unfastened and for whatever reason, she's taken his boots and socks off. "What happened?"

"I put you under; got you on the table; tied you up; put you on the monitor; took a look at your heart with the echo machine; went and analysed that blood sample I took earlier; tidied stuff up in here… It's amazing what you can get done in a couple of hours." She sounds surprisingly nonplussed, although he can still see the red line of the cut down her cheek and feels a jolt of guilt.

"I don't know what came over me. I am sorry…"

"You've said." She genuinely doesn't seem to care. "And I think you do. Know what came over you, I mean." Her pointed glance at the Mark tells him she has it figured out.

"Yeah, I…" He changes direction when he looks down at himself again. "You mind explaining that?"

"Oh. Yeah. I was checking your pulse points. Your radial pulse vanished so I had to make sure. There's a couple of pulse points in your feet and then your femoral artery."

His eyes widen. "Excuse me?"

"Don't worry, I didn't cop a feel. I don't go for that."

"You jumped at the chance to get my pants open."

"Yeah, well. It helps your circulation." She gives him a slightly mocking look. "I'm sorry, does that make you uncomfortable? Because being attacked by someone I'm trying to help makes me uncomfortable."

Suitably admonished, he lets it drop. Tentatively, he tests the straps around his wrists again. "Any chance you could take these off now? I think I've done my Hulking out for the day."

She gives a dry laugh. "Uh, no. I don't think so. Not until I'm sure you won't go off the rails again."

"I'm feeling calmer."

"Your heart rate's still as high as it was before you flipped out the first time." She nods towards the monitor, where he can see his heart's still beating more than eighty times a minute. As if he couldn't feel it anyway. "I'd rather not get into another scrap. I've only just got everything tidied up."

"You know, you're stronger than you look."

"So are you." He doesn't know what kind of look he gives her in response to that until she chuckles. "That wasn't meant as an insult. I can kick the shit out of most rowdy demons without breaking a sweat, but you… You put up one hell of a fight."

"Yeah, well… I've got this thing supercharging me." He lifts his right arm until it's stopped by the restraints. "What's your excuse?"

"I've already told you, if you've been paying attention."

He thinks for a moment. "What was it? 'An ongoing experiment in organic alchemy'?"

She gives him a condescending smile. "Clever boy."

Once again, her attitude grates on him. "Alright, so…how long until I can get out of here?"

She doesn't answer immediately. Instead, she gets up and crosses round the table until she's standing on his right hand side, observing the monitor screen. "That all rather depends. Guy your age, in good shape…your resting heart rate should be in the sixties. It hasn't dropped below eighty since you got here. And until it does…I don't know that you aren't gonna go all crazy violent on me again."

This is starting to get frustrating. He balls his fists and then flexes them as he lets out a steady breath, trying to ease the tension building in his chest. It's a fight not to get angry. "Yeah, well. You were about to inject me with a needle full of you-didn't-say-what and you're keeping a tray of surgical tools right next to me. That may have been a trigger point."

It's not quite an outburst, but it gets her attention. She turns to fix him with a cool stare. "I'm working out of an unfinished loft conversion with two equipment carts and one room I can keep sterile. Cut me some slack. It's not like I don't end up using them 90% of the time. In case you've forgotten, you're not my usual clientele."

"Well, an explanation would still have been nice."

"Demons don't usually demand that either."

He shoots her a scowl, but getting into an argument isn't likely to get him out of the cuffs faster. Trying to calm down, he gives a huff and closes his eyes. "What was in the needle, then?" he asks after a couple of seconds.

"Contrast agent," she states drily, and when he opens his eyes again he can see she's leaning on the table. "For the echocardiogram."

He gives her a blank look.

"Heart ultrasound," she clarifies with a roll of her eyes. "I was intending to do it while you were still conscious. Still… there's one thing I am curious about." She glances down at his arm, then back up at his face. He's surprised to see most of the hostility has gone from her expression. "Most demons don't even get the power of self-healing. When you were a demon…did you have a heartbeat?"

He's taken aback, but supposes the question makes sense. "I…" Now that he's contemplating it, he isn't sure. "I think so." All he can remember is the way it was pounding as Sam tried to heal him. The rest of the time…if it had been there, it was too slow to notice.

"Hmm. Interesting…" A thoughtful look settles on her face as her eyes lower to his arm, careful and scrutinizing. She reaches out to gently press two fingers to the Mark, almost caressing his skin. "Then I think this is only one of your problems."

He winces, the contact prompting another dull twinge of pain. A heavy weight seems to have settled in the pit of his stomach, though he doesn't know what he'd expected to hear. "Great. This the part where you give me the bad news?"

There's another pause. She glances over at the monitor screen, noting his heart rate has bumped up another notch, and then meets his gaze. He figures she's not one for breaking this to him gently. "There's tissue damage to your heart. Here." She taps over the center of his chest again. "Scar tissue showed up on the echo in the right ventricle, making it stiff and resistant to contraction. Also damage to the valve, causing tricuspid regurgitation. I think you have getting stabbed to thank for that."

Half of those words weren't even English to him, but he gets the gist that it's bad. She doesn't give him chance to ask questions before continuing.

"From the EKG, looks like there's increased electrical permeability in the calcium channels in your heart. My guess is that's down to the demon cure, which should have decreased the sulfur levels in your blood. Maybe by purging, or through chemical reactions to convert it into innocuous compounds, such as calcium sulfate. However, from your bloodwork, you've got increased levels of both calcium and sulfate ions, as well as trace amounts of pure sulfur in your blood, which says to me the Mark's trying to convert you back into a demon and your body's fighting it off. That also seems to explain why the Mark's pushing your body into overdrive. I took your temperature earlier…"

His eyes widen then, glancing down at his conspicuously open belt, and she smirks. "Orally. Quit panicking, Winchester. But the point is it shouldn't be 100.2 degrees. You should be running a fever, but you're not. Your body's baseline temperature has been altered, and it's down to this." She taps the Mark again. "Everything's working too hard and too fast. Combine that with the structural damage to your heart, and I'd say the palpitations you've been having have been atrial fibrillation. Your heart wants to beat faster, but the scar tissue's resisting, hence arrhythmias in the atria and the vanishing radial pulse. All that together, and…" She draws a breath. "It's gonna burn you out."

Most of it was babble to him, but that final line made perfect sense. His stomach plummets even further. "You're saying…it's gonna kill me?"

"The Mark wants you as a demon. That means it has to stop your heart first. And I don't know how long it will take, but…yeah."

He hadn't been expecting her to break it to him gently, but she does at least seem a little sorry to say it. He closes his eyes and draws a deep breath, allowing that to sink in. Each heavy heartbeat in his chest seems like a taunt. "Right. Well, you're the doctor. So what can you do?"

He looks up at her again, almost hopeful, but she looks impassively back. "I don't know. Buy you more time, I guess. Maybe try some medication for the arrhythmias, but that tissue damage is gonna need surgery."

Just great. He tastes bitterness on his tongue. After everything Sam went through to cure him, and now this. All he knows is that he can't go back to being that again.

"I could do the surgery, if you wanted," she continues, oblivious to his reaction. "Done it plenty of times on demons. Just give me a week to get hold of a bypass machine, and I could…"

"I'm good, thanks," he cuts her off, his chest feeling tight. He doesn't know why he rejects it so certainly, though part of him is wondering if Cas could help. But with the angel's grace already running so low, Dean can't ask this of him.

"Medication, then." She turns to one of the trolleys, rifling through the bottles of medication on the bottom shelf, again ignoring the look of desperation on his face. He clenches his jaw, not really listening. "Here. Try this." He's jolted back to the present by the feeling of her pressing something to his lips, and a second later he realizes it's a pill. His mouth opens without thinking, and she pushes it in.

"Do I not get a glass of water?" he complains, tasting the real bitterness of it, and she just raises a mocking eyebrow.

"No. Now just swallow. Or is your gag reflex gonna be a problem?"

He scowls back, but does as he's told.

"Beta blockers. Let's see how that pans out," she says, turning her attention back to the monitor screen, and he finds himself following her gaze.

"You think that can help?"

"With the palpitations? Yeah. Should bring down your resting rate."

A couple of minutes pass, Dean's mind reeling, Carter just calmly watching the numbers on the monitor screen fall, then she gives a satisfied nod. "Sixty-nine. Good enough," she says, then smirks. "Alright. You can get dressed now." Her attention turns to finally unfastening the restraints, and he can't move to get up fast enough as she pulls the stickers off his chest and then frees his wrists. Fortunately, she seems to have no interest in watching while he puts his clothes back on, more concerned with tidying away her equipment.

When he's finally done and turns back to her, she's holding out a bottle of pills to him. "Here. Atenolol. Should last you between one month and three, depending on how often you get the palpitations. One a day, and one more if you feel an episode coming on. Go up to two a day if it doesn't help."

Somewhat warily, he accepts the bottle off her. "And how much are they gonna cost?"

She smirks again. "Let's call them free. It's not like I paid to get hold of them anyway."

He raises a cautious eyebrow at that. "And the consultation?"

Another smirk. "Let's call that free, too. Don't wanna clean you out on your first visit."

Whatever motive she has for that, he doesn't know, and he eyes her suspiciously. "You sure about that? Even with the…" He motions awkwardly towards her cheek, feeling another wave of shame.

"I'm sure. You were a pretty interesting case, actually. Save your money for the surgery."

"I'm not gonna have the surgery."

She shrugs. "Sure. But in case you change your mind…" She holds her hand out to him, a slip of paper gripped between her index and middle fingers. He guesses she wrote it while he was getting dressed. "Call ahead next time."

He briefly considers declining, considering how unpleasant the whole ordeal had been, but something compels him to reach out and take it. "Alright. Thanks, doc."

"No problem." She still has that goddamned smirk on her face, and he wishes he knew why.

"So, uh…I'll see myself out, then?"

"You do that." He can't tell if she's mocking him or not. "See you around, Winchester."

He just grunts gruffly and turns to walk away, unable to get out of there fast enough. He can feel her eyes burning into the back of his skull right until he turns the corner, and even then it feels like she's watching him right until he leaves the apartment. Still, he can't exactly call the whole thing a waste. The bad news is only slightly sweetened by the pill bottle resting in the inside pocket of his jacket, but it is hope, and in the end, it hadn't even cost.

Now he just has to get back to the bunker and hope Sam doesn't question where he's been.