Meg, my second Cavalier, lived happily and actively with a Grade 4 murmur for 3 years, only picked up when she had a thorough vet check in preparation for flying from South Africa to the UK with me. No external symptoms, no medication. What tipped her over into CHF was a week of appalling air quality, when even walking round the house and garden was like pushing through thick porridge and it just put too much strain on her heart, though even then she lived and enjoyed life for nearly another year. So no races up mountains for Daisy this holiday - but enjoy it all of you, human and canine, you all need a real break.
Kate, Oliver and Aled