I am so sorry to hear about your dog. To answer your questions:
1. How could her regular vet have missed this. He sees her twice a year most recently two months ago.
Heart disease can be silent for years until it gets to the point that 1) a murmur develops or 2) the dog shows clinical signs (as yours does). Your vet probably never heard a murmur and therefore had no reason to suspect heart disease. Think about how humans suddenly have a heart attack without warning.
2. How quickly can she deteriorate.
It depends on the type, how advanced it is, and if it can be slowed (not fixed unfortunately) with medications. The range would be months to several years.
3. What can I do to keep her comfortable until tomorrow morning.
NO ACTIVITY; even carry her outside to potty.
4. What does this diagnosis mean, what is the treatment and what will the treatment do for the quality of her life
Did they test her for heartworms? If she was negative, then a cardiac ultrasound is the only way to know what type it is and if medication will significantly help.
The heart is enlarged because it is a muscle that has been working overtime to try to keep up.
Medications include diuretics (to make her pee and make it easier for the heart to push the blood) and sometimes drugs to improve the strength of each beat.
Treatment will improve her quality of life because she will not have such a hard time breathing and will have more energy.
Your next step is to have the ultrasound and possibly an EKG done to see what medications they can start.
Take it easy today, and see your vet first thing tomorrow. They will probably want to start medications until an ultrasound can be scheduled.
Best wishes,
Dr. T
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