DOG CARE

Why Almost 75% of Senior Dogs Have Some Form of Heart Disease

Last updated: August 24, 2026 · Written by Sam, Founder

A veterinarian using a stethoscope to examine a senior Golden Retriever on an exam table

Mitral valve disease affects most dogs by their mid-teens, and most cases go undetected. Here's what actually happens and which signs matter.

Heart disease affects about 10% of dogs overall — but that number climbs sharply with age, reaching roughly 75% of dogs past 9 years old. Most of those dogs show no obvious symptoms. The gap between how common this is and how rarely it gets talked about comes down to one fact: in its early and middle stages, canine heart disease is often silent, detectable only through a stethoscope during a routine exam most owners assume is just a formality.

The Condition Behind the Statistic

The overwhelming majority of senior-dog heart disease is one specific condition: myxomatous mitral valve disease (MMVD), which accounts for roughly 75% of all cardiovascular disease diagnosed in dogs. MMVD is a slow, degenerative thickening of the mitral valve — the valve controlling blood flow between the heart’s left atrium and left ventricle — that gradually loses its ability to seal completely. Each incomplete seal lets a small amount of blood leak backward, forcing the heart to work harder to compensate. In one study, mitral valve insufficiency was present in as many as 75% of dogs by age 16.

This progresses over years, not weeks, which is exactly why it stays hidden for so long. A dog can carry a mild, asymptomatic leak for a long stretch of its senior years before the workload catches up with the heart enough to cause visible symptoms.

A veterinarian and dog owner examining a senior dog together in a veterinary clinic exam room — Early mitral valve disease usually has no visible symptoms — a heart murmur on exam is often the only clue.

Why So Few Cases Get Noticed Early

Only around 10% of dogs with heart disease progress to the severe stage — congestive heart failure — that produces symptoms owners would actually recognize as a problem: a persistent cough, especially at night or right after lying down; labored or faster breathing at rest; reduced stamina on walks; occasional fainting or collapse; or, in advanced cases, a visibly distended abdomen from fluid buildup.

Before any of that, the only detectable sign is usually a heart murmur — an abnormal whooshing sound caused by the leaking valve, audible only through a stethoscope during a physical exam. This is the practical argument for not treating senior wellness visits as optional once a dog is symptom-free: the murmur that gets caught at a routine checkup is often the only warning available before the disease has progressed significantly. If you’re weighing what a senior dog’s vet visits and any resulting workup actually cost, see our breakdown of what senior dog vet bills look like.

Which Dogs Are Most at Risk

MMVD disproportionately affects small and toy breeds. Cavalier King Charles Spaniels are the breed most strongly associated with it, often developing valve disease earlier and more severely than other breeds — see our Cavalier-specific breakdown of vet costs and heart disease for what that looks like for this breed specifically. Chihuahuas, Poodles, Dachshunds, and Cocker Spaniels also carry elevated risk. Larger breeds aren’t immune to heart disease, but they’re more associated with a different condition — dilated cardiomyopathy, which weakens the heart muscle itself rather than a valve — so breed matters for which condition to watch for, not just whether to watch at all.

A veterinarian using a stethoscope to listen to a French Bulldog's heart during a clinic exam — Small and toy breeds carry most of the elevated risk, but the stethoscope check is the same routine step for every senior dog.

What This Means Practically

None of this means a senior dog with a newly detected murmur is in immediate danger — most dogs live with early-stage MMVD for a long time with no impact on quality of life, sometimes managed with medication once the disease progresses far enough to warrant it. What it does mean is that “no symptoms” isn’t the same as “no heart disease” in a dog past about 9 years old, and that the annual or twice-yearly senior exam is doing real diagnostic work even when nothing about the visit looks eventful. If a murmur is found, the usual next step is monitoring — periodic rechecks, sometimes imaging — rather than immediate treatment, since timing intervention correctly matters more than starting it early for its own sake.

The Bottom Line

Heart disease in senior dogs isn’t rare, and it isn’t usually dramatic — it’s a slow, common, largely silent process that a stethoscope catches long before symptoms would. The statistic worth remembering isn’t just that 75% of senior dogs are affected; it’s that the disease stays undetectable to an owner for most of its course, which makes the routine vet exam the actual early-warning system, not anything visible at home.

This article is for informational purposes only and does not replace guidance from your veterinarian.

FAQ

How common is heart disease in senior dogs?

Heart disease affects roughly 10% of all dogs but becomes far more common with age — studies have found it in around 75% of dogs over 9, and mitral valve insufficiency specifically in as many as 75% of dogs by age 16. The most common form, myxomatous mitral valve disease (MMVD), accounts for about 75% of all canine cardiovascular disease and is especially common in small and toy breeds.

If it's this common, why don't more senior dogs show symptoms?

Most don't, at least early on. Only around 10% of dogs with heart disease progress to severe disease or congestive heart failure, which is the stage that typically produces visible symptoms like coughing, labored breathing, or exercise intolerance. Early-stage valve disease is usually only detectable through a vet hearing a heart murmur during a routine exam — which is one of the strongest arguments for not skipping senior wellness visits.

What is mitral valve disease, specifically?

It's a degenerative thickening and weakening of the mitral valve, the valve between the heart's left atrium and left ventricle, that causes it to leak blood backward with each heartbeat instead of sealing fully. Over years, that leak forces the heart to work harder and can eventually enlarge it. It progresses slowly in most dogs, which is why it's often present for a long time before it's severe enough to cause symptoms.

What are the warning signs of heart disease in a senior dog?

A persistent cough (especially at night or after lying down), faster or labored breathing at rest, reduced stamina or reluctance to exercise, fainting or collapse episodes, and a distended abdomen in advanced cases. Earlier than any of these, a heart murmur detected during a routine vet exam is often the first and only sign — which is why regular senior checkups catch this well before symptoms would.

Which dog breeds are most prone to heart disease?

Small and toy breeds — Cavalier King Charles Spaniels most notably, along with Chihuahuas, Poodles, Dachshunds, and Cocker Spaniels — are especially predisposed to mitral valve disease, with Cavaliers often developing it younger and more severely than other breeds. Larger breeds are more associated with a different condition, dilated cardiomyopathy, which affects the heart muscle rather than the valve.