Living With a Dog in the Pre-clinical Stage: Monitoring and Rechecks

Being told your dog has a heart murmur, and then being told the plan is simply to "keep an eye on things", can feel strangely unsatisfying. You came in worried about your dog's heart, and you are leaving with no tablets, no procedure, and an appointment for some unspecified point in the future. It is natural to wonder whether watching and waiting really counts as doing anything at all.

It does, and it is exactly the right thing to be doing. The stretch between a murmur first being heard and your dog ever showing a symptom is called the pre-clinical phase, and in mitral valve disease it commonly lasts for years (Borgarelli and Buchanan, 2012). For most of that time your dog is genuinely well: eating, playing, sleeping and behaving completely normally. Your job during this window is not to treat a sick dog. It is to keep a calm, light-touch watch so that the moment anything begins to change, you and your vet catch it early. This article is the practical handbook for that role. If you have not yet read the ACVIM staging guide, it is worth a look first, because the whole monitoring plan is built around which pre-clinical stage your dog is in.

The pre-clinical years: normal life, light-touch vigilance

Let us start with the reassurance, because it is real and it is earned by the evidence. Mitral valve disease typically progresses slowly. A great many dogs carry a murmur for years before anything else happens, and a meaningful proportion never go on to develop heart failure at all during their lifetime (Borgarelli and Buchanan, 2012). A murmur is a reason to pay attention, not a countdown clock.

"Pre-clinical" simply means before any clinical signs. Your vet may have placed your dog in stage B1 (a murmur with a heart that is still a normal size) or stage B2 (a murmur with a heart that has enlarged, but still no symptoms). Those two stages are managed differently, and the difference matters: a stage B2 dog will usually be started on a medication called pimobendan, because a landmark trial showed this delays the onset of heart failure, whereas a B1 dog is monitored without medication (Boswood et al., 2016; Keene et al., 2019). I will not re-tread that decision here, because the stage B2 and EPIC trial article covers it in full. What unites both stages is the daily reality: your dog feels well, and your role is watchful, not interventional.

The mental shift that helps most owners is this. You are not waiting helplessly for something bad. You are building a baseline. The more you know about how your dog looks, breathes and behaves while they are well, the more obvious it will be if that ever shifts. That baseline is the single most powerful monitoring tool you have, and you are the only person who can build it.

Counting the resting respiratory rate: your early-warning number

If you take one practical habit away from this article, make it this one. Counting your dog's resting respiratory rate, the number of breaths they take per minute while genuinely asleep or resting quietly, is the most useful thing you can do at home throughout the pre-clinical phase and beyond. It is free, it takes thirty seconds, and a rising trend is often the earliest sign that fluid is starting to build in the lungs, frequently before your dog looks unwell to you (Boswood et al., 2018; Porciello et al., 2016).

I will not explain the counting technique in detail here, because the resting respiratory rate guide owns that end to end, and the breathing rate tracker lets you log each count and actually see the trend over weeks rather than relying on memory. What matters for the pre-clinical owner is why you are doing it at this stage at all.

The point is the baseline again. In a healthy resting dog, the rate usually sits comfortably below around 30 breaths per minute (Rishniw et al., 2012). But your dog's own normal might be 16, or 22, and knowing that personal figure is what makes a future change meaningful. A reading of 28 means something completely different in a dog whose baseline is 16 than in one whose baseline is 26. So even though your dog is well, start counting now, perhaps a couple of times a week, and let the tracker remember the pattern. You are not looking for a single alarming number. You are learning the shape of "normal" so that "different" becomes visible.

The recheck rhythm: what your vet is watching, and how often

Alongside what you do at home, your vet will want to see your dog at intervals, and the rhythm of those rechecks is not arbitrary. The 2019 ACVIM consensus statement recommends that dogs with a murmur but no heart enlargement (stage B1) are typically re-evaluated around every 6 to 12 months, because the thing everyone is watching for is the day the heart begins to enlarge, which is the signal that the plan needs to change (Keene et al., 2019).

What is the vet actually looking at during these visits? Three things, broadly. First, listening: is the murmur louder, and is the heart rhythm still regular? Second, imaging, which is where the real answers live. Chest x-rays let your vet measure heart size objectively, often using a standardised measurement called the vertebral heart score, which compares the heart's dimensions against the dog's own spine so that change over time can be tracked reliably (Buchanan and Bücheler, 1995). An echocardiogram, a heart ultrasound scan, gives a more detailed picture of how stretched the left atrium and left ventricle have become, and it is the test that most precisely distinguishes B1 from B2. Third, a general check that nothing else has crept in, such as a heart murmur changing character or signs of another problem.

How often imaging is repeated depends on your dog's stage and how stable things look. A settled B1 dog might have a scan or x-rays roughly once a year; a B2 dog, already closer to the turning point, is often monitored a little more closely. The exact interval is a conversation to have with your own vet, because it is tailored to your dog. The useful thing to understand is that these rechecks are not a formality. Each one is a deliberate look for the specific moment the disease moves forward, so that treatment can start at the right time rather than too early or too late.

This is also why a recheck schedule is worth keeping even when your dog seems perfectly fine. The whole value of the pre-clinical phase is that change is caught while your dog still feels well. Skipping rechecks because "nothing seems wrong" defeats the point: the entire aim is to find the change before anything seems wrong.

The signs that would move things forward

Between visits, there are specific things worth noticing, and knowing them turns vague worry into useful watching. The change that matters most, and the one your home counting is designed to catch, is a sustained rise in the resting respiratory rate. A breathing rate that climbs above your dog's baseline and stays there, particularly if it pushes consistently above around 30 breaths per minute at rest, is the most important early signal that the disease may be progressing, and it warrants a prompt call to your vet (Boswood et al., 2018; Porciello et al., 2016).

Other changes worth flagging include new tiredness or a drop in stamina, such as your dog tiring sooner on a familiar walk or being less keen to play; increased breathing effort even when the rate looks normal; restlessness or difficulty settling at night; fainting or a sudden collapse; and reduced appetite. A cough deserves a particular note, because it causes a great deal of unnecessary panic. Not every cough in a dog with a murmur is heart failure, and in fact a cough in a pre-clinical dog often is not the heart at all. The differential is genuinely worth understanding, so rather than half-explain it here, I will point you to is it a heart cough or an airway cough?, which owns that question properly.

To be clear about urgency, because owners often ask: a sudden onset of fast, laboured, distressed breathing is not a routine recheck matter, it is an emergency, and it is covered in recognising a heart failure crisis. A gradually rising resting rate over days, by contrast, is a "ring the practice in the next day or two" situation, not a midnight dash. Knowing which is which is part of what makes the watch-and-wait role manageable rather than anxious.

Exercise, weight and dental health in the meantime

A frequent and understandable question is whether a dog in the pre-clinical phase should be wrapped in cotton wool. For most dogs the answer is a relieving no. There is no good evidence that normal, self-regulated exercise harms a dog with pre-clinical mitral valve disease, and keeping your dog fit and active is good for them in every other way. Let your dog enjoy their usual walks and play, simply allow them to set the pace and stop when they want to, and avoid pushing them into prolonged exhaustion or strenuous exertion in the heat. Sensible activity is part of a good life here, not a risk to be eliminated.

Weight is where you can make a real, active contribution to your dog's heart. Carrying excess weight makes the heart work harder and makes breathing less efficient, and obesity is an avoidable burden on a heart that already has a leaking valve to contend with. Keeping your dog lean is one of the most genuinely useful things you can do during the pre-clinical years, and it is entirely within your control. Your vet can help you find and hold a healthy body condition.

Dental health deserves a mention too, because it links to the heart more directly than many owners expect. Dental disease is extremely common in the small breeds that are most prone to mitral valve disease, and good dental care matters for overall wellbeing. If a dental procedure under anaesthetic is ever needed, it is well worth telling your vet about the heart condition in advance so the anaesthetic can be planned appropriately; a stable pre-clinical dog is generally not barred from necessary dental treatment, but the team will want to know.

For the wider picture of feeding a dog with heart disease, including the sensible role of salt and the evidence on supplements, diet and the heart is the place to go, because it owns that ground in full and there is no need to duplicate it here.

The thread running through all of this is that watch-and-wait is an active, hopeful role, not a passive one. You are building a baseline, counting breaths, keeping your dog lean and active, and showing up for the rechecks that are designed to catch change early. Done well, it can mean years of good, ordinary life before anything else is needed, and it means that when the picture does eventually shift, you and your vet are ready. The single most likely next chapter, the moment an enlarged heart turns watchful waiting into early treatment, is the subject of the stage B2 and EPIC trial article, and it is the most empowering thing you can read while your dog is still well.