"I can drive tractors, feed out, cook tea ... I'm feeling good."
His saviour came in the form of a white butterfly-shaped clip, no bigger than a 20c coin, named the MitraClip by US developers Abbott Vascular.
During the three-hour procedure, performed through Midland Cardio Vascular Services at Braemar Hospital, it was guided through a tiny incision made in his groin, into his femoral vein and up into his heart.
Mr Williamson was still in the theatre when he instantly felt the improvement; he told the surgeons: "I can breathe again."
Two days later, he walked 500m around the hospital with little discomfort.
Within a week, he was cooking mutton chops at his bach at Mokau.
"I couldn't believe it, myself ... and I don't think the hospital staff could either," he told the Weekend Herald. "People used to hear me breathing down the phone when I talked. They don't now."
The condition affects people who have had heart attacks, are older or who have rheumatic fever.
As a teenager, he was operating a dairy factory vat when a huge electric shock sent him across the floor.
The jolt also caused his heart to expand, something further complicated as his body eventually grew.
When he came to have major heart surgery in 1992, a surgeon assumed he had been born that way.
"The back quarter of my heart had been sheared off ... like it had been docked like a lamb's tail."
Though he managed to lead a busy, active life, operating a fleet of trucks and running a farm, his condition troubled him to the point where he could do no more physical work.
After learning about the technology, he decided that paying $86,000 for the procedure was worth getting his life back.
"You can buy a new car and you're happy for a day. This way, I'm happy for a lot longer."
Dr Rajesh Nair, who led the surgery team, saw the procedure as a major milestone for heart patients, offering hope for those for whom open-heart surgery was not an option.
The procedure has been performed more than 10,000 times around the world, and has been available in New Zealand for several years, but only in the private sector.
There are now calls for it to be made available publicly for Kiwi patients, with Mr Williamson backing them.
"I'm more than happy to support the push. I can't believe how well I feel, but I'm sure there are many other people out there in New Zealand who just can't afford it."