The 29-year-old Scarlets and Wales prop had been on an exercise bike in the gym at Parc y Scarlets in January when he began to feel dizzy, which was soon followed by chest pains.
Thomas, who had a heart attack while with previous club the Newport Gwent Dragons in 2006, was treated by the Scarlets' medical staff before being rushed to Morriston Hospital in Swansea where he underwent a life-saving quadruple heart bypass.
While Thomas' recovery is progressing well, he still experiences breathlessness when walking and is on a special diet and fitness regime.
The seven-cap forward would like to continue to work in the sport at which he reached the highest level, but is focused on completing his recuperation, which could take another 12 months.
"I'm going to get myself healthy and back to some sort of normality," he said.
"I don't have any plans but hopefully there will be something out there.
"I would like to stay in rugby in some capacity but I am open to anything."
Thomas paid tribute to the support he had received from his family, the Scarlets and the wider rugby community following his heart attack and realises he is lucky to be alive.
He said: "I was extremely close to losing my life.
"My surgeon tells me that when he opened my chest he did not think I would make it through the operation.
"When he was telling me things like that in the days before I went home, that's when it really hit home that it was that close.
"But I am still here so I am pretty happy.
"I have had a couple of weird incidents through my life but I am using up my nine lives definitely, I don't think I have many left."
Thomas' retirement is the second by a Scarlets' prop this week after former Wales loosehead Iestyn Thomas hung up his boots due to a neck injury.
And the 35-year-old, who won 33 Wales caps and made 214 appearances for the west Wales region, believes the demands of the modern game may mean that lengthy careers like his own, which stretched back over 15 seasons, may become a thing of the past.
He said: "Professionalism means players are getting bigger and stronger so the collision side of the game is getting heavier, that's the way things have gone.
"I think you will see players come into the game at a younger age and finish younger.
"I have been fortunate to have the career I have had. But if you look at guys like (Wales wing) George (North), he is 20 and I can't see George playing at 35.
"I think players will play for 10-year periods but that will probably be it."
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