Your heart pumps blood around your body at 80-100bpm.
But when Tim Warner suffered a cardiac arrest during the final leg of the Run Norwich 10k his heart was beating at more than four times this speed.
He has since been diagnosed with a heart abnormality that doctors have never seen on a living patient.
He is lucky to be alive.
Mr Warner, a 53-year-old father of two from Dereham has spoken out about his experience, and thanked the paramedic who 'leapt' to his aid.
Mr Warner said: 'I was doing the 10k run and it was going really well. I was feeling healthy and high-fiving kiddies as I ran.
'I thought I'd give it a bit of a finish, and I suddenly felt really dizzy and down I went.
'My initial reaction was: 'oh, I've just fainted'.
MORE: Run Norwich 2017: Drama as off-duty paramedic rushes to help runner who has heart attack
'I saw all these faces around me and tried to sit up and felt pain in my chest.
'Someone said: 'Your heart's stopped mate, you can't go anywhere'.'
Luckily, off-duty paramedic instructor, Dale Gedge, 34, who lives in Norwich city centre, was watching the race, after returning from holiday a day early.
Mr Warner continued: 'Dale leapt over the fence and gave me immediate attention.
'Another paramedic - one of Dale's pupils - rushed over with a defibrillator. A few minutes after that armed police arrived with a medic bag.'
Mr Warner praised the organisers of the event for having everything in place.
He said: 'The Run Norwich team were fantastic. It's an absolutely brilliant event.
'I was very lucky it happened where it did, at the end of the race. If I'd been back by Carrow Road where there are fewer people around, I might not have made it. Somebody was smiling on me.'
After receiving CPR and first aid, Mr Warner said he, 'came around quite quickly and was very alert.'
He said: 'My ribs were hurting - the thing with CPR is that if you're doing it properly it should be breaking your ribs.
'I was lucky Dale was there and wasn't afraid to go in and smash my chest up. I'll be indebted to him for the rest of my life.
Mr Warner, who runs a van rental company in Dereham, is now at home with his wife, Rebecca. He was discharged from hospital after eight days, and expects to make a full recovery.
However, his collapse was due to a heart abnormality that has been undiagnosed since birth, known as coronary disposition - both his left and right arteries enter the heart on the same side.
'I was giving it some welly at the end of the race, and that strangled the aorta and cut off the blood supply to my heart.
'I'm an active sportsman: I run, I bike, and I go to bootcamps.
'A doctor said to me: 'what probably put you in here was your running, but what saved your life was your level of fitness'.
'When I had the angiogram, the consultant got the image up on a screen and said: 'Mr Warner you're a very lucky man'.
When he saw the abnormality he said 'you're a doubly lucky man'.
'I can't get my head around it. There are no case studies of this anywhere so the doctors are getting very excited.
'A team of surgeons are getting together to discuss my case. It's never been seen on someone who's still alive.
'They're debating what to do - a bypass, another surgery or fitting me with a mini-defibrillator.
'After what I've been through I know I'm in great hands.
'The survivor rates of CPR are not very high. Not very many people come out without brain damage, and without strokes.
'Apart from my broken ribs I feel absolutely wonderful. I'm the luckiest man alive.
'I'm in a lot of pain but so grateful to be here. I feel like I've won the lottery 10 times over. What good is money if you're dead? I'm one of the luckiest people on the planet.'
Mr Warner praised the care he received from the NHS. He said: 'From the minute I collapsed to the hospital, the attention, professionalism, care and knowledge from everyone was remarkable. From the cardiac ward staff and the doctors to the cleaners who were so friendly - our NHS is awesome.
'I am feeling really positive - I'm the happiest man alive. What have I got to moan about?
'I'm a happy person by nature - that should stand me in good stead. The healing process is aided by a happy heart.
'I was saved for a reason, and if I can do anything its making people more aware of the importance of CPR and first aid.'
'Extremely grateful and proud' - Race organisers praise hero paramedic
Emergency services and event organisers have praised the quick thinking of an off-duty paramedic who saved a man's life at the Run Norwich 10k.
Dale Gedge, 34, works as an instructor for the East of England Ambulance Service.
Organisers of the Run Norwich 10k have said they are: 'extremely grateful to Dale and proud of our event medics and marshals who all worked together to save Tim's life.
'Tim has spoken to us to express his thanks, and we have remained in contact with him and his family since the event.'
The East of England Ambulance Service echoed their thanks and said: 'It is important to emphasise that what Dale did – performing CPR - could be done by anyone and can be learnt by anyone.'
The service is currently urging schools to sign up to Restart a Heart Day so that more people can learn CPR.
MORE: Schools in Norfolk and Suffolk urged to sign up to lifesaving lesson
Paramedic encourages public to learn CPR skills that saved man's life
The danger during a cardiac arrest is that your organs can be starved of oxygen.
As paramedic Dale Gedge explained, that's why Tim Warner was so lucky.
Mr Gedge said: 'The main part of your body that needs oxygen is your brain.
'Because Tim received CPR almost immediately he won't have had any kind of oxygen deficit.'
He explained: 'I was with him within 10 seconds, and opened his airway within 30 seconds.
'We were using the defibrillator on him within a minute to 90 seconds.
'In another minute to a minute-and-a-half, his heart was beating again - and he was sat up and wondering what all the fuss was about.'
Mr Gedge said that as every minute passes, during a cardiac arrest, the patient's chance of experiencing a poor outcome increases by 10pc.
He encouraged the public not to be afraid to perform CPR, and said: 'Its always better than doing nothing'.
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