There are few better places to have a cardiac arrest than on a Premier League football pitch thanks to the level of medical support on hand. Speed is of the essence and the sooner cardio-pulmonary resuscitation (CPR) is started, and the heart shocked back into a normal rhythm to restore circulation, the better. The longer the delay the greater the risk of damage to the brain.
Cardiac arrests in athletes like footballers are rare but well documented, and Muamba is not the first player to collapse on the pitch - in 2007 the Sevilla midfielder Antonio Puerta arrested in the penalty box and, despite the best efforts of the emergency services, died in hospital three days later.
Cardiac arrests are different from classic heart attacks. When a person arrests their heart either goes into chaotic rhythm, or it stops altogether. Either way the net result is the same, blood no longer circulates to the nutrient-hungry brain and the person loses consciousness immediately.
Heart attacks, on the other hand, are caused by a blockage in the blood supply to the muscular heart wall and are often a much slower process. They tend to start with crushing chest pain and normally occur in older people, and, while the resulting insult to the heart can cause rhythm disturbances and lead to cardiac arrest, it doesn’t always do so.
Top athletes tend to have healthy arteries and are at very low risk of heart attack, but the pressures of training and competing at the highest level can bring hidden electrical glitches to the fore. This is why all UK professional footballers now undergo careful testing (ECG and an echocardiogram) to screen for such tendencies.
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Muamba will have been tested but screening is not infallible - problems can still be missed and, rarely, footballers with an outwardly normal heart can still be prone to electrical instability when subjected to intense physical demands.
It is now a matter of waiting. Standard protocol in those who survive arrest after a lengthy period of CPR is to anaesthetise and cool them in intensive care for 24 to 48 hours to reduce swelling of the brain and speed recovery. It is only after this period that any long-term damage can be properly assessed. It will seem an eternity for friends and family.