A leading cardiologist yesterday raised doubts about the medical screening which Premier League footballers undergo after it failed to detect the problem which led to Fabrice Muamba's collapse at the weekend.
Doctors worked for two hours to get the Bolton Wanderers midfielder's heart beating again after he slumped to the ground a few minutes before half-time during the match against Tottenham Hotspur.
Sanjay Sharma, professor of cardiology at St George's Hospital, said: "I am surprised the heart problem was not picked up. The medical screening these players get is extremely comprehensive. It will identify 80 per cent of conditions causing sudden death."
The hospital, in Tooting, south London, runs Britain's only cardiac unit for sportsmen and women and has screened 20,000 athletes.
Messages of support poured in for the Wanderers and former England under-21 player, who remains anaesthetised and in a critical condition in hospital. Former teammate Gary Cahill wore a T-shirt with the words "Pray 4 Muamba" written across it, which he unveiled after scoring for his current club, Chelsea, yesterday.
Bolton's next scheduled opponents, Aston Villa, agreed to postpone their forthcoming match as a mark of respect.
Sadly, the sympathy shown by the footballing community was not universal. A man was arrested yesterday on suspicion of racially abusing Muamba after a message was allegedly posted on Twitter and later deleted by a 21-year-old from Pontypridd.
"Our thoughts are with Fabrice's family and Bolton Wanderers and we are all willing him to pull through. Events such as this put everything into perspective," said Daniel Levy, chairman of Tottenham, Bolton's opponents in the FA Cup quarter-final tie.
Muamba, 23, was taken to the London Chest Hospital after collapsing in the 41st minute of the match. He received prolonged resuscitation at the ground and on the way to the hospital, where doctors got his heart working.
The fast response of the medical team at Tottenham's White Hart Lane ground was praised by experts.
Dr Graham Stuart, an FA-accredited cardiologist, said Muamba's chances of recovery were significantly aided by their speed in reaching him and beginning attempts at resuscitation.
"They were obviously very troubling scenes but the thing that was most vital was how quickly he received treatment," he said.
"At that stage the support is critical and the speed of treatment is vital. Any delay can damage organs."
Undetected heart defects affect about one in 500 young people. Most live normal lives unaware that anything is wrong. But in elite sportsmen and women who push their bodies to the limit, a defect may make itself felt suddenly with devastating effect. That may explain Muamba's collapse.
If he survives the next few days the worry will be the effect of the minutes he lay on the pitch and in the ambulance while his brain was deprived of oxygen. His chances are improved by the speed with which the paramedics began working on him.
But the outcome will depend on how successful they were at keeping his blood circulating while his heart had stopped.
The commonest heart defect is cardiomyopathy, an inherited condition that causes thickening of the muscle in the heart wall, compressing the left ventricle and leaving no space for the blood to be pumped.
But cardiomyopathy can be hard to distinguish from "athlete's heart", the enlargement of the heart that occurs as a result of training, which is natural and a sign of fitness. This is especially so in black athletes.