Myxomatous Mitral Valve Disease (MMVD) in Weimaraners

The mitral valve sits between the heart's left atrium and left ventricle, closing tightly with each heartbeat to keep blood moving in one direction. In myxomatous degeneration, the valve's tissue slowly thickens and becomes floppy, so it no longer closes completely. That imperfect seal lets some blood leak backward into the atrium with each beat — the sound of that leak is the murmur your vet hears.

Over time, the heart compensates by enlarging to handle the extra volume of blood, which works for a while but eventually becomes less efficient. This is a genuinely progressive disease at the tissue level, not just a sound that stays the same — which is exactly why staging and periodic re-imaging matter more here than a single snapshot diagnosis.

Veterinary cardiologists commonly use a staging system running from A (at risk, no disease yet) through B1 and B2 (a murmur is present, with B2 meaning imaging shows the heart has started enlarging in response) to C and D (heart failure has developed, either previously treated and stable or currently decompensated). This staging isn't just academic — it directly determines when medication starts.

A dog in stage B1, with a murmur but no significant heart enlargement, is often just monitored with periodic rechecks rather than started on medication immediately. Once imaging shows stage B2, with meaningful enlargement, many cardiologists recommend starting medication proactively, since research has shown this can meaningfully delay the onset of heart failure. Once a dog reaches stage C, additional medications targeting fluid management typically join the treatment plan. This staged approach is why 'my dog has a murmur' and 'my dog needs medication today' are often two different conversations.