The 500,000th pacemaker operation in the UK has taken place - at the same hospital, St George's, London, where the first procedure was carried out in 1958.
BBC News website readers have been telling us how pacemaker technology has changed their lives.
Last Tuesday marked the 30th anniversary of my first pacemaker, which was implanted when I was a mere 18 months old at Great Ormond Street. I don't know if I was the youngest person to have one implanted at that time, but it was certainly not common for a child of that age to have one then. I'm now on about my seventh!
I had my first pacemaker implanted at the Royal Victoria Hospital in Belfast when I was 22 years old. It has made an extremely significant improvement in my quality of life. The difference between my first operations and the more recent one, last August, is immense. The size of the new pacemakers and the improved procedure has made recovery easier. It has helped me to live a normal life.
I am a nurse working within cardiology and by coincidence have also had a pacemaker for the past 22 years. I had my first pacemaker inserted aged 25 which was a bit of a shock, but have gone on to lead a normal life, have four children and work more than full time in a busy NHS.
I have had eight pacemakers since 1973. The early ones lasted two and half years, and were large and heavy. Problems with wires and infections meant my first pacemakers had to be changed frequently. The first one only lasted 24 hours and the first five years were very problematic. Modern ones are smaller, lighter and can be changed less often. I have had a biventricular pacer since 2003 and can say that it saved me from being considered for a heart transplant.
David Cornforth, Exeter
According to Guinness World Records, my wife had the oldest working pacemaker in the world when she ran the London Marathon two years ago to celebrate her 50th birthday. She still has the same one today. In the past 27 years she has had two perfectly healthy children, won a national sailing championship and written a book as well as raising over £5,000 for the British Heart Foundation running the marathon. She is a senior school teacher and will be highly embarrassed to find that I have provided these comments!
Kevin, Westcliff-on-Sea, Essex
I've had a pacemaker now for over 20 years. It was fitted at St George's when I was in my twenties. The pacemaker has never affected anything I do - I swim, cycle, cross country ski and fell walk. The only thing I would have liked was the opportunity to speak to someone of my own age when I was about to have the first pacemaker fitted.
Helen, Fleet, Hampshire
I had my first pacemaker fitted in November 2007 to improve a slow heart beat. Within hours of the operation I felt a rejuvenating warmth in my hands, feet and face. As a result I was able to think more deeply and actually enjoy exploring my mind.
Martin, Ipswich, Suffolk