LONDON (AP) -- Sprinter Sacre, one of Britain's top racehorses, has been diagnosed with an irregular heartbeat following medical tests.
The 7-year-old steeplechaser visited equine specialist Celia Marr in Newmarket on Saturday after pulling up during his seasonal debut on Friday, ending his unbeaten record over fences.
Sprinter Sacre's trainer, Nicky Henderson, says the horse has atrial fibrillation and that Marr will wait until early next week to see if the situation stabilizes.
Marr also worked on Denman, a former Cheltenham Gold Cup winner who had a similar heart complaint.
Henderson says ''in her opinion, the reason for these situations is that both horses are supreme athletes and they are more likely to suffer from these problems due to the size of their hearts, which in both cases are unusually large.''