Its owner, Lesley Strong of Yardley Hastings, says the impotency medication has given Talisker a "new lease of life" after the border collie developed a dangerously enlarged heart from a lung infection.

Three-year-old Talisker passes out whenever he gets excited because his blood cannot pump fast enough around his body.

Vets warned he could die from the condition. Then Ms Strong was told by a leading animal cardiac specialist that the little blue pill might do the trick and keep her pet alive.

Ms Strong, 58, who lives with partner Danny Green, said: "We were very surprised when we were recommended Viagra.

"It causes great hilarity at the chemist's when I pick up the prescription."

She added: "His heart is under pressure and Viagra improves blood flow to the heart.

"He is happy and healthy apart from the heart. I'm pretty sure it has kept him alive, but, the thing is, it can't cure him.

"He needs special care and we have to make sure he doesn't over exert himself, as over-exertion causes it.

"It's about him being active without being over-exercised."

The dog – named after a single malt whisky manufactured on the Isle of Skye, with Sky also being his mother's name – fell ill in June last year.

It was believed Talisker contracted lungworm, which led to the infection.

Ms Strong, a retired pub landlady, said: "We were told that there wasn't much we could do about it. We were then referred to a specialist."

Talisker now takes one quarter of a Viagra tablet three times a day and an eighth of an aspirin daily, following the advice of Hertfordshire veterinary doctor Nat Whitley.

Ms Strong, who also has a golden retriever, called Oliver, said: "He is my little star.

"I don't know what I would do without him. Both my dogs are my boys."

oliver.jelley@northantsnews.co.uk