Saving someone's life is an experience few of us will ever have.
But in recent years a team of volunteers - known as First Responders - have meant the difference between life and death for thousands of people.
Responders are spread across the county with individual groups based in Windsor, Slough and Maidenhead. Most have full-time jobs but when on call they can be summoned from their homes or places of work like retained firefighters.
They carry essential equipment including a defibrillator and oxygen and can reach a nearby patient before the paramedics arrive.
Responders from across Berkshire were gathered as usual this week at the ambulance station at Wexham Park Hospital for their regular training session.
Fran Brewer, 51, from Stoke Poges got her first call out in February, months after becoming a Responder.
She said: "A man had suffered a cardiac arrest really close to where I was. I was first there. I did not restart his heart but had given him the first shock and started the compression process on his chest when the paramedics arrived.
"Death is a process not something that happens in a moment, our job is to delay that process until the paramedics get there."
Fran worked in the pharmaceutical industry organising clinical trials and now runs her own consultancy business.
Lee Docherty, 41, from Cippenham, Slough, started as a Responder nine months ago.
Lee, who is married with an 11-year-old daughter, said: "My mum was a nurse and when she died I decided I wanted to put something back into the community.
"I have been to 244 calls in nine months. It was nerve racking first time but you are warned not to get emotionally involved.”
Ronald Davies, 50, of Windsor is an IT projects manager. He started as a Responder last year and got his first call on Friday - to a man of 70.
He said: "Two of us were the first on the scene. I went into automatic mode and did the things I had been trained to do.
"It was only later I sat down and relived the day's events in my mind."Jo Hempshall, 25, of Slough had some practical advice to all Responders - 'always bring a spare top. I needed it when a baby was sick on me."
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