As an assist to recognizing MVD emergency signs, I will give examples of Darcy's behavior for the symptoms listed in Lessons Learned Part 1:

1) discomfort exhibited by restlessness or the inability to get comfortable;
Darcy would move from spot to spot never staying more than several minutes in any one spot. Sometimes she would lie on her side, then sit up and then lay on her stomach all in the same spot and all within a short time. She would try to lie in our laps but would get down within a few minutes.

2) shallow and more rapid breathing (panting). Anything above 30-35 breaths per minutes is too rapid;
No explanation needed. Count the breaths. Too many, take your cavalier in.

3) visible heartbeat due to an enlarged heart;
Darcy's heart was so enlarged her body would "bounce" in time with her heartbeats when she was lying on the floor. Also, we could feel a very strong heartbeat when she would lie in our laps. Your cavalier might not visibly exhibit such an enlarged heart but if you can feel it just by lightly placing your hand on your dogs chest it's pretty strong.

4) a look of worry or panic (this is due to an inability to get enough oxygen either through restricted breathing or cardiac output);
Sometimes the look is interpreted to be "spacy" rather than worried or panicky but it is definitely not a usual alert look for a cavalier. The eyes may seem to not focus on anything in particular.

5) labored, raspy, or "wet" breathing sounds.
Darcy's breathing would sound wet, almost as if she had a chest cold, but there wouldn't be any sneezing. There was also the classic "hacking (or gagging) cough" which had been ongoing for a while.