Please, please order an EF genetic DNA test from aht.org.uk. It only costs £48.00
Get your vet to take the two swabs (to positively identify the dog and its microchip to the result) and then post the swabs back to AHT. Whilst it takes a while for the kits to arrive, you will get the results back within days. The Lab technician emailed the certificates to me as PDF's.
It is probable that your vet will not know anything about EF. Alfie has had EF since 2007 but I have only recently been able to confirm it with the DNA test.
If you know who the breeder is then you can write to them advising that their breeding stock has EF. If they test all their stock then they can remove the condition entirely from their stock
For advice and discussions on health issues please take a look at Cavalier Chat. http://www.cavaliers.co.uk/forums/
Whilst a number of them are breeders they do have years of health experience and years of looking after cavaliers.
Alfie has a mild case of EF, and so long as I don’t let him get over excited then he is absolutely fine. But I know of other people whose dogs are on medication for this condition