What it is
In a healthy heart the right ventricle pumps blood to the lungs, and an orderly electrical signal keeps every beat in step. In this disease the muscle wall of the right ventricle is slowly replaced by fat and scar-like tissue, which carries that signal poorly. The heart then fires extra beats from the wrong place, sometimes in runs, and for a moment it can stop pumping blood as it should.
The disease is inherited and develops in adult dogs, slowly and without warning. A dog can show nothing at home for years, and the rhythm changes may come only in short bursts.
Between episodes an affected dog can live a full, ordinary life. It helps to notice how your dog copes with running, play and excitement, and to write down any wobble or faint: when it happened and what the dog was doing just before.
Signs you may notice
You may notice the dog suddenly becoming weak, staggering or fainting, especially while running or excited, or tiring sooner on walks. If a dog has fainted or collapsed, it needs a vet immediately.
When to see a vet
If your dog faints or suddenly collapses, it needs a vet immediately. If it tires sooner than it used to or has brief wobbly spells, book a visit so a vet can check the heart.
This is general information, not veterinary advice. For your own dog's health, tests and treatment, see a vet.