The programme for Hong Kong Cup winner Vengeance Of Rain has been thrown into disarray after the discovery of a heart irregularity yesterday forced his withdrawal from Sunday's Group One Stewards Cup. Trainer David Ferraris called in the vets after the gelding's morning work was below form yesterday and head clinical vet Chris Riggs diagnosed an episode of 'atrial fibrillation' in the World Racing Championship title-holder. The racing stewards panel immediately ordered the horse's withdrawal from Sunday's Triple Crown first leg. 'His work wasn't up to his usual standard so I had him checked to see if there was a problem and this has come up,' Ferraris said. 'It's made things more difficult from a programming point of view because, even though the mile of the Stewards Cup was going to be too short, I wanted him to run as a lead-up to the Gold Cup. I'll just have to see how he is before we know where we go next.' The only races for which Vengeance Of Rain is now eligible between Sunday and the Hong Kong Gold Cup (2,000 metres) on February 26 are the Centenary Vase (2,000m) on February 5 and a Premier Class mile race on February 11. 'As far as the horse is concerned, well, I'm not sure what to think because I never had [this condition] in a horse in South Africa and have only had one moderate Class Five horse with it here,' Ferraris said. 'Who knows? Maybe he has had it before, maybe not. Anywhere else, you'd just look at his gallop and say it was poor work and that would be that, but with the vets on site here and everything investigated so minutely you find these things are discovered more often.' Riggs said the condition was common in horses, for various physical reasons including the size of their hearts, and said the 'outlook is favourable for a return to normal, as long as there are no other serious health issues with Vengeance Of Rain'. 'The remedy at this stage is rest and close monitoring of the horse,' Riggs said. 'Some horses just go back to normal and some require treatment but there's no rush to do anything until we see how he progresses.'