Champion trainer Nicky Henderson reports Sprinter Sacre to be "very bright" as he prepares to undergo crucial heart tests in Newmarket later this morning.
Simply unbeatable in 10 previous outings over fences, Sprinter Sacre made his eagerly anticipated seasonal return in Friday's Desert Orchid Chase at Kempton.
All appeared to be going well for National Hunt racing's brightest star when he produced a long and flamboyant leap at the fifth, but just two fences later jockey Barry Geraghty suddenly applied the brakes and trotted back anti-clockwise around half a circuit before dismounting in front of Henderson and concerned connections.
Vets quickly discovered the seven-year-old was suffering from an irregular heartbeat and after a comfortable night back at Henderson's Seven Barrows base, he is now on his way to be assessed by Celia Marr, a specialist in equine internal medicine and cardiology.
Speaking on Channel 4 Racing's The Morning Line, Henderson said: "The only thing we know at the moment is that he did have an irregular heartbeat and that is what we're concentrating on. It's the only explanation.
"It is something that, as far as we are aware, has never been part of his vocabulary. It obviously never was last year and it hasn't been (this season) as far as we know.
"His work and everything at home has been as exceptional as always.
"He came home last night and left here soon after 6am this morning to go to Newmarket, where Celia Marr is awaiting him. We thought about going last night, but we got him home to his own bed, rather than staying away.
"He's been out this morning, he ate up last night, was very bright and wanted his breakfast. We trotted him up and he's perfectly sound.
"This is obviously a clinical situation that has arisen. It's not a physical problem."
Sprinter Sacre's comeback was delayed after he was ruled out of the Tingle Creek Chase at Sandown at the start of December following an unsatisfactory scope.
Henderson is adamant the two problems are not linked.
"He didn't have a virus. He had a bacterial infection. He never missed a day's work and wasn't sick during that period. It was just a set of unsatisfactory figures, so we couldn't run him (at Sandown)," said the trainer.
Denman is a recent case of a top National Hunt horse recovering from what is often known as atrial fibrillation.
The 2008 Gold Cup hero had an operation to correct a problem that September and although he was beaten on his racecourse return the following February, he was capable of finishing second to Kauto Star back at Cheltenham and winning the Hennessy a few months later.
Henderson said: "Talking to Celia Marr last night in quite a lot of detail, you take Denman and Sprinter Sacre and they are both big horses and hugely talented horses.
"When you get into the situation of what you might call superior athletes, they probably do all have big hearts. Big hearts are great things to have, but they also can cause problems, simply because there is more of it and things that can go wrong with it.
"He's got a 10am appointment with the heart specialist and we hope to know more today. When we know any more, we will obviously keep everybody posted."