Work Text:
During early diastole, the semilunar valves are closed, the atrioventricular valves are open, and the whole heart is relaxed.
It is late (or early) and Tony just can’t sleep.
He might not be a biologist (metal is predictable [relatively predictable {somewhat predictable}], blood and muscle are messy), but time and circumstance have given Tony Stark every reason to be familiar with the function of the human heart.
Next comes atrial systole where the atrium contracts forcing blood from the atrium into the ventricle.
The arc reactor glows in the dark room. The blue light is cold and sterile, illuminating the faces of his bedmates through the sheet. They both look so young when they sleep. Well, they look so young asleep right now - it could change in an instant.
Nightmares are a fairly regular occurrence in this bed. Trauma upon trauma upon trauma will do that to a person.
The muscles in the ventricle contract, but the blood remains in the chamber. This is the first stage of ventricular systole, also referred to as an isovolumic contraction.
Pepper can take up more space in the bed than Bruce and Tony combined when she wants to. Tonight, though, she stays close.
He shifts, his head resting on Bruce’s chest. He listens to the beat of Bruce’s heart (immediate auscultation, less reliable for diagnostic purposes than mediate or Doppler auscultation, but wonderfully soothing in the depths of the night), filing the sensation of Bruce’s chest hair against his skin away in the back of his mind (it is soft and a little bit coarse, it catches in Tony’s stubble).
In the second stage, blood is forced from the heart pushing open the pulmonary and aortic semilunar valves. Ventricular relaxation, or diastole, follows repolarization of the ventricles.
Bruce makes a sleepy noise and cuddles closer to Tony. He half opens his eyes and smiles down at Tony.
“Go back to sleep,” Tony whispers, turning his head to press a kiss to Bruce’s chest.
The beat of a human heart is made up of two sounds - S1 and S2. S1 occurs when the atrioventricular valves close at the beginning of systole.
Bruce’s fingers trail gently over Tony’s shoulder, but his eyes close. Pepper is snoring quietly (adorable snoring, and he will never ever tell her). She shifts closer again, and Tony will never stop being surprised by how soft and smooth her skin is.
He can feel her heart beat through her breast, steady and strong (just like Pepper).
S2 is the second sound. The semilunar valves close, blocking flow reversal. It occurs at the end of ventricular systole and the beginning of ventricular diastole.
She throws her arm over Tony, her fingertips rests on Bruce’s belly. Tony doesn’t even try to stop the satisfied sound that bubbles up from deep within his chest.
He can feel the heartbeat of the two people he loves most in the world (two of the people he loves most in the world - try as he might, Rhodey just isn’t interested in whatever this puppy pile of fucked upedness and feelings is [he is still Tony's best friend though, even if he has terrible taste]), a tangible reminder that, for now, they are safe and well.
The heart sounds are caused by turbulence as the atrioventricular and semilunar valves snap shut to prevent the regurgitation of blood between the ventricles. It reverberates within the heart chambers.
Tony takes a deep breath. He catalogues everywhere he is touching Pepper and Bruce (everywhere, he is touching them everywhere). He focusses on how their skin feels, how their sweat feels. He makes a note of how they smell, how they sound.
He is impossibly warm and safe here, cocooned in his bed with the people who make his life worth something. The vicious thing that usually keeps a tight fist around his own heart eases its grip as he feels the rhythm of Bruce and Pepper’s heartbeat.
Maybe tonight, he would sleep.