http://www.isabellevets.co.uk/health_advice/dog/info/roundwormsdog.htm

"Until recently Heartworm caused by Dirofilaria immitis has not been a problem in the United Kingdom. However two factors are changing this situation and we should all be warned about the possibilities of this fatal parasite, especially if we live or travel in mainland Europe or live in southern Britain."

There ya have it I guess.....