Mr Knowles was taken to the nearby Royal Devon and Exeter Hospital, where he suffered a further cardiac arrest and a pulmonary embolism.But his condition improved after having three stents fitted to open his arteries, along with an internal defibrillator implanted in his chest.Mr Knowles spent five weeks in hospital and is now recovering at home after defying the expectations of medical professionals who initially told his family to expect the worst.Doctors are convinced his survival is down to the rapid first aid he received from the woman in his audience. She thought I was role playing, but I told her it was real and that I was going to lose consciousnessDavid Knowles David Knowles with his wife Nova, also a retired nurseCredit:SWNS She said: “I was there while the paramedics were resuscitating David. He was in and out of consciousness and I was worried he would be afraid, but he was very calm and telling them exactly what was wrong. He was so calm and clear because he was directing us.” Want the best of The Telegraph direct to your email and WhatsApp? Sign up to our free twice-daily Front Page newsletter and new audio briefings. A first aider talked one of his church group trainees through saving his life after he suffered a cardiac arrest during a class on how to deliver CPR.David Knowles, a retired nurse, was delivering a talk about his work with the St John Ambulance when he found himself at the centre of a real-life emergency.The group thought the 77-year-old was role-playing, before realising the severity of the situation as he began to lose consciousness.A woman in the audience went to help Mr Knowles, who told her exactly what to do to save his life before he passed out.She gave the St John Ambulance trainer CPR until an ambulance arrived at the Belmont Chapel church group in Exeter, Devon. Mr Knowles fell ill on February 16 and was discharged from hospital on March 22.Doctors at first feared he might have suffered brain damage and that his internal organs could have been affected by his ordeal.They also predicted he would need months of rehabilitation, but Mr Knowles was allowed home several weeks earlier than expected.He is now being looked after by his wife, 75-year-old Nova, also a retired nurse. Mr Knowles, a retired nurse who has volunteered with St John Ambulance for 11 years, said: “I had just started my lecture.”We were talking about cardiopulmonary resuscitation – CPR – and the more senior members of the group had asked for a demonstration. As I was instructing one of them, I suddenly felt dizzy and weak, so I had to lie down.”She thought I was role playing, but I told her it was real and that I was going to lose consciousness. I told her what to do to save my life, then passed out.”I’m told I came too, briefly, and was talking to the paramedics about my condition, but the next thing I remember is waking up in hospital, two and a half weeks later.