Cambridge revealed yesterday that the reason Shane O'Mara, the United States international oarsman, had been removed from their crew for tomorrow's Xchanging Boat Race was that he had been suffering from an irregular heartbeat.

O'Mara was taken for testing at Addenbrooke's Hospital in Cambridge on Wednesday, where a diagnosis was made of atrial fibrillation, the commonest form of cardiac arrhythmia, which affects 1per cent of the population.

Cambridge had initially refused to discuss the medical reasons for O'Mara's withdrawal but Duncan Holland, the head coach, said yesterday: “This condition is not uncommon among top athletes and can normally be controlled by medication. Unfortunately, in Shane's case, there were some minor complications and it was decided not to allow him to race.”

O'Mara is in the first year of a three-year course in land economy, so there is every chance he will be able to compete next year. He may draw comfort from the example of Rob Waddell, a New Zealand rower who won an Olympic gold medal in the single sculls, the most gruelling rowing class, in 2000, three years after receiving the same diagnosis. Waddell recently came out of retirement to attempt to qualify for the Beijing Olympics this summer, but suffered an atrial fibrillation during the final race of a qualification series with Mahe Drysdale, the world champion. Waddell was last week awarded a place in New Zealand's double scull for the Olympics.

Ryan Monaghan, a 23-year-old from New York State, was given O'Mara's stroke seat in the Cambridge crew, lowering the average age of the eight to 24. The youngest man in the boat will be Tobias Garnett, 20, of Trinity College, who is the only undergraduate in either crew.

“Rowing in this race was a dream since I was quite young,” Garnett said. “I went to King's College School in Wimbledon and our boathouse is the one that Cambridge use for the race, so from a very young age I had these goliaths walking around showing how rowing was done, and you can't help but aspire to that.”

Garnett rejects suggestions that the Boat Race is demeaned by the lack of undergraduate rowers. “On average, rowers peak later, so postgraduates are bound to be better and there are now far more of them than there were. The coaches have a large base to select from,” he said. “It's important that the race keeps its standards high by selecting the best rowers.”

In 1914, Garnett's great-great-uncle, Kenneth, rowed in the Cambridge boat that beat Oxford by 4 lengths. “Five of his boat died fighting for their country within a couple of years,” Garnett said. “It's fairly awe-inspiring.” It also places the inconvenience of a treatable heart condition in context.

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