A medical trial to discover whether it is possible to extend the lifespan of pet dogs has shown early signs of success.
On average, domestic dogs live for between 10 and 13 years, although the world record is 29 years.
Wild dogs live longer than household pets, so scientists are confident that the animals are capable of greater lifespans.
Evolutionary geneticists at the University of Washington in the US have been conducting preliminary trials to see if rapamycin, an anti-rejection medicine given to kidney transplant patients, could ward off death.
The drug has been shown to extend the life of mice by more than a quarter.
If it was found to have a similar impact in canines, it could potentially help them live for an extra four years.
The first trials were conducted on 24 middle-aged golden retrievers, Labradors and German shepherd dogs to see if adding low doses of rapamycin to their food could improve their health and slow ageing.
The initial phase was intended simply to show that the drug was safe to be administered, without side effects. But scientists have seen heart improvements.
"The key findings are that there were no significant side effects associated with the rapamycin treatment, and there were statistically significant improvements in heart function in the dogs that received rapamycin relative to those that received the placebo - similar to what has been observed in older laboratory mice," said Dr Matt Kaeberlein, the director of the healthy ageing and longevity research institute at the University of Washington.
"It is important to keep in mind that this is a small study that requires replication before we can be confident in these results.
"It is also important to recognise that we don't have any evidence that the improvements in heart function indicate overall improvements in health or slower ageing in these dogs or even what the long-term effects of rapamycin will be.
"We are finishing the analysis of the data for the dogs that completed the phase 1 study and hope to submit the results for publication within the next few months."
The researchers said the results were "highly encouraging" and provided "strong justification" for new trials which will last between three and five years.
Rapamycin has an antiinflammatory effect and also helps cells get rid of waste, clearing rubbish from the body.