It was a unique moment. I stood in the operating theatre at Papworth Hospital holding in my hands the artificial heart machine which had kept a man alive for two years.
It had beaten probably 3 billion times or more, propelling the blood through his body to vital organs like his lungs, kidneys and liver.
A few weeks before surgeons had removed it in a 15 hour operation and replaced it with a donated human heart.
Matthew Green's was a difficult operation. The human body doesn't like bits of plastic implanted in it. It reacts by forming scar tissue.
In the theatre, Steven Tsui, the surgeon who carried out the operation, told me Matthew's artificial heart was completely enveloped in scar tissue. It's tough stuff. It took five hours to cut it away and Matthew bled profusely.
He spent days in intensive care - an operation like that affects the kidneys and other organs
He was fighting for life. Dr Tsui told me it was touch and go for a couple of weeks.
But when I walked round Papworth's lawns and duck pond with Matthew, his wife Gill and seven-year-old son Dylan, he was smiling a lot.
He had a walking stick but hardly needed it. He was still having dialysis because of the effects of the operation on his kidneys. But he was bathed in an new feeling of freedom and optimism.
Two years ago, it was very different, For a year before that Matthew's heart had been feeling, gradually getting worse. He told me one week he could only walk the length of the ward. The next week, he could only manage to walk the width of the ward.
In the summer of 2011, doctors at Papworth offered him a lifeline. A mechanical artificial heart that would replace his failing heart until a donor could be found. He had little choice.
It would mean risky surgery. It would mean carrying in a rucksack the pump that powered the implanted mechanical heart - everywhere he went 24 hours a day. There would be risks of infection, of the device not working properly. But he would be alive.
Now, after his transplant, Matthew can say goodbye to the rucksack. It had become an almost intolerable burden. It was noisy - a continual ker-thump. People in restaurants asked if he could turn it off. It kept him awake. It was depressing.
But after two false alarms, when doctors told Matthew there might be a donor heart for him but then had to stand him down, he finally got the transplant operation.
Now, he's looking forward to the future - cycling and kicking a ball around with his son Dylan.
Dylan says he wants to go swimming with his dad. As we part, Matthew is taking Gill and Dylan for a pub lunch in the sunshine, With a bright future ahead.