Think about the last time he flopped down beside you and you put your hand on his side.

You felt it. That steady thump under your palm. It's so ordinary you probably didn't think about it for even a second.

Here's what nobody says out loud: that muscle has been doing that his entire life. No breaks. Not one, ever, since before he was born.

Every other muscle in his body gets time off. His legs rest when he lies down. His jaw rests between meals. Even his breathing gets easier when he sleeps.

One muscle never does.

Your dog's heart beats somewhere around 100,000 times a day. It doesn't get weekends. It doesn't get to sleep in. It has been the hardest-working muscle in his body since day one, and it's working right now while he snores on the rug.

And muscles that work that hard all have one thing in common: they carry the biggest fuel bill in the body.

Nobody sells you anything for that. There's no ramp for it. There's no chew shaped like it. The whole senior dog aisle is built around what you can watch him struggle with — the stairs, the stiff mornings, the walk that quietly got shorter.

The muscle doing the most work is the one you'll never see.

That doesn't mean anything is wrong with your dog. It means there's a part of how dogs age that almost nobody bothers to explain — and it's worth ten minutes to understand it.

• At rest it beats roughly 70 to 120 times a minute — faster than yours, for his whole life
• That works out to around 100,000 beats a day, and somewhere near 36 million a year
• It has never taken a break. Not for a second, not once, not since before he was born
• Of every organ in his body, it carries the highest non-stop energy demand
• It runs almost entirely on energy made inside the cell, so it can't coast the way other muscles can
• Cells make that energy in tiny power plants called mitochondria — and heart muscle is packed with more of them than almost any other tissue
• Those power plants need a helper molecule called NAD+ to do their job, and NAD+ naturally declines as dogs get older

Read that list again and notice something. Not one line on it is about a problem.

It's just how the body is built. The heart is a muscle. Muscles run on energy. This one runs on more energy than anything else in there, and it never gets to stop and refill.

Now put the last two lines together, because that's where it gets interesting.

Cells make energy in mitochondria. Mitochondria need NAD+. And NAD+ goes down as dogs get older — that part is well documented. Older cells also lose it faster, because an enzyme called CD38 climbs with age and burns through the supply.

Less made. More spent. Every year.

Every tissue in the body feels that. But the one with the biggest bill feels it the way you'd feel a pay cut if you had the highest rent — first, and hardest.

That's the whole idea. Not that something is broken. That the hardest-working muscle in your dog is running on a smaller budget every year, and nothing in the pet store aisle is pointed at it.

One important thing before we go further. This article is about normal aging and the energy that cells run on. It is not about heart conditions, and Pawprint Protocol is not a treatment for any of them. If your dog is coughing, tiring far more easily than usual, breathing oddly at rest, or if your vet has ever mentioned anything about his heart, that is a conversation for your vet — not a supplement.

Walk down the senior dog aisle and count what's on it. Joint chews. Hip formulas. Mobility bites. Skin and coat. Calming treats.

Every single one is aimed at something you can watch happen.

That makes sense — those are the things that worry you, so those are the things that sell. But it means every product clusters around the visible half of aging, and nobody in that aisle is asking the more basic question: what is the energy all of it runs on, and what happens to that supply over time?

Here's what's going on underneath.

Inside almost every cell in your dog's body are mitochondria — tiny power plants that turn food and oxygen into usable energy. Heart muscle is loaded with them, far more densely than most tissue, because it has to be. It never gets a night off to catch up.

Those power plants need NAD+. It's a helper molecule involved in hundreds of everyday jobs inside the cell, energy production being the big one. Without enough of it, the plants run slower.

And NAD+ falls with age. Meanwhile CD38, the enzyme that consumes it, rises. So the supply gets squeezed from both ends at once.

None of that shows up as something you can point at. It shows up as a slow change in what he's got in the tank — the walk he used to do without thinking about it, the recovery that takes an extra day now, the enthusiasm that's still there but doesn't last as long.

The tank didn't break. It just doesn't fill the way it used to.

Pawprint Protocol was built by dog owners who got tired of buying products aimed at symptoms and wanted to support the thing sitting underneath all of them.

Working with veterinary advisors, they built a daily liquid around one job: give cells the building block they use to make NAD+, and deliver it in a form that actually gets absorbed.

The lead active is NMN. It's the direct building block for NAD+, and it's the one ingredient in the formula with published dog research behind it — oral NMN has been studied in dogs and raised NAD+ levels in the liver.

Then there's the part most supplements quietly skip.

A lot of what you sprinkle on dinner never actually makes it into the dog. Stomach acid, first-pass loss in the liver, ingredients that don't dissolve well on their own — the label promises one thing and the cell receives another. If you've ever finished a bottle of something and honestly couldn't tell whether it did anything, this is usually why. That wasn't your judgement failing. It was a delivery problem.

Pawprint Protocol is a liposomal liquid. Each active is wrapped in a tiny fat-based shell that helps it survive the trip, so more of what's in the dropper reaches the cells that use it.

A few drops on the food he already eats. That's the whole routine.

That's really the point of this whole article.

For his legs, you have options. A ramp. A set of steps. A runner down the hallway. You can build your way around the problem.

For the muscle in his chest there's no workaround to buy. There's no gear for it. The only thing anyone can actually do anything about is the energy supply the cell draws from — and that's the same supply every other hard-working tissue in his body is drawing from too.

That's what Pawprint Protocol is for. Not a fix for anything. Support for the cellular energy the heart muscle runs on, and the rest of him along with it.

Four actives, each with a job:

• NMN: The direct building block cells use to make NAD+, the helper molecule that naturally declines with age. The hero of the formula, and the one with published dog research behind it.
• NAD+: Included as part of the same pathway, supporting the cellular energy system every working muscle draws on.
• Resveratrol: A plant compound studied alongside NAD+ for its role in the cell's energy and repair signalling.
• CoQ10: Sits inside the mitochondria — the tiny power plants where energy actually gets made.

All four in a liquid built to absorb, which is the part that decides whether any of it arrives.

✔ Supports the cellular energy the heart muscle runs on
✔ Supports the cellular energy that naturally declines with age
✔ Supports healthy energy and stamina in senior dogs
✔ Works alongside any food — kibble, raw, fresh or home-cooked

Made for dogs 7 and up. Pawprint Protocol is a supplement, not a medicine, and is not intended to diagnose, treat, cure or prevent any disease. Individual results may vary.

Here's the honest version of this section.

You are not going to see his heart change. Nobody can — not you, not us, not from the outside. Anyone telling you otherwise is selling you something they can't stand behind.

What owners actually report is simpler, and more useful: stamina. How much he's got, how long it lasts, and how fast he bounces back afterwards. That's the visible edge of the same energy supply this whole article has been about.

This is the pattern owners describe most often. It's what people tell us, not a clinical result. Individual results may vary.

Easy to miss at first. A sudden trot down the hallway for no particular reason. Getting up to follow you into the kitchen when he'd normally have stayed put. One owner told us the first thing she noticed wasn't the walk at all — it was that he came to the door when she picked up her keys, which he hadn't bothered doing in months.

Most owners have quietly shortened the route over the last year or two without ever deciding to do it. This is usually where that stops. Same loop, and he isn't asking to turn back at the halfway point. A few have told us they went back to the longer route on purpose, just to see.

This one is less about the activity and more about what happens after it. The big afternoon at the park used to cost him the whole next day flat out on the floor. Owners often mention around here that the recovery day gets shorter — or stops being a thing at all.

By now the good days stop standing out, because most days look like that. That's usually the point where people stop keeping track.

After three months the goal changes from noticing to keeping. NAD+ keeps declining with age, and that muscle keeps working every second either way, so the dogs who hold their ground tend to be the ones who stay on it.

Individual results may vary. Check with your vet if your dog is on medication, or if anything about his energy changed suddenly rather than gradually.

You've spent his whole life listening for him. The paws on the floor at 6am. The sigh when he finally settles. The thump under your hand when he leans into you on the couch.

That last one has been running non-stop since before you met him, and it has never once asked you for anything.

You can't buy it a ramp. But you can support the cellular energy it runs on — the same energy everything else in him runs on too.

Reviews are unedited excerpts from verified Pawprint Lab customer reviews and describe general energy and vitality, not heart function. Individual results may vary.

[1] You, J. et al. Subacute Toxicity Study of Nicotinamide Mononucleotide via Oral Administration. Frontiers in Pharmacology, 2020;11:604404.

[2] Camacho-Pereira, J. et al. CD38 Dictates Age-Related NAD Decline and Mitochondrial Dysfunction Through an SIRT3-Dependent Mechanism. Cell Metabolism, 2016.

[3] Age-Dependent Decline of NAD+ — Universal Truth or Confounded Consensus? Nutrients, 2022.

[4] Mitochondrial Aging and Age-Related Dysfunction of Mitochondria. BioMed Research International, 2014.

[5] Katz, J. et al. Improved owner-assessed cognitive function in senior dogs receiving a senolytic and NAD+ precursor combination (n=70). Scientific Reports, 2024.

[6] Jiang, Y. et al. Therapeutic potential of nicotinamide mononucleotide in regulating canine NT-proBNP levels. Journal of Advanced Veterinary and Animal Research, 2026;13(1):11-18.

[7] Network Physiology in Aging and Frailty: The Grand Challenge of Physiological Reserve. Frontiers, 2021.