Thank you all for your kind words and thoughts - I was stunned to see how many posts there were for our girl and that so many of you have a soft spot for her

I've had a much needed good cry, (even Sophie was looking at me as if to say "good grief women get over it I'm still here"), a good talking to from my level headed dad about not getting overwrought when pregnant and dh & I are accepting that we just have to take every day as it comes with her - we know she is an old boxer now we just weren't expecting to get this news when outwardly she seems to have been doing just fine.
Sophie got her first dose of medication last night - her dinner was delayed a few hours as her stomach has to be empty before getting the capsule. Now Sophie has a very regular tummy bell so was most unhappy, she mumped, huffed, shuffled from side to side, snorted and I'm sure she and Dino were about to break out the phone book to call the RSPCA to report us for neglect by the time she could get fed
I guess there's no chance he was listening to her heart just after her shot, not before?
No, he did check it beforehand - I was just so surprised as outwardly she has been the same as always - bit slow on her weekend walks (she refuses to go out at 6am with us during the week

) with her arthritis but she's been at the same pace for about a year now. Her heart was listened to on a previous vet visit a couple of months ago and there was no audible change then. I guess I'm just clutching at straws that there is another reason for this and not the logical one that she is simply wearing out.
Another thought - just possibly it might be worth asking your vet if he thinks it worthwhile to refer her to a specialist. The Queen Mother Hospital for animals just north of London has some of Europe's best cardiac specialists on staff. I have never used vetmedin, but they have a useful looking website:
http://www.vetmedin.co.uk/index.php
We have talked this through to a degree with the vet - they do have a cardiologist who can be booked to come to their surgery to see her so we're needing to have a good talk through with the vet on her check up visit next week when our brains are actually in gear and not gone blank like yesterday! Thanks for the info on the website too.