Several Wales players sent messages of support on Twitter to the 27-year-old who was a bricklayer last season before getting his break with the Newport Gwent Dragons.
He then earned his Wales debut as a replacement against the Barbarians in June before going to start against England at the Millennium Stadium and Namibia in the Rugby World Cup.
But he would never get to appear for Wales in the RBS 6 Nations with his last game of rugby coming in the RaboDirect PRO12 against the Ospreys on December 30.
And WRU Head of Rugby, Joe Lydon, said: "All of us involved in Welsh rugby want to pass on our best wishes for the future to Lloyd after his sadly enforced retirement from the sport.
"We can only imagine his disappointment especially given the incredible recognition he has earned at the top level of the sport in Wales over the past year in particular.
"Of course the most important issue for Lloyd is his continued good health, but he can look back on a playing career in which he truly proved his potential.
"Apart from winning his caps, one important legacy he can be proud of is how he proved to us all that the standard of rugby being played in the Principality Premiership here in Wales can equip players to achieve their potential at the highest level."
Burns' retirement comes within three months of another Wales front rower, Rhys Thomas, having undergone heart surgery in January.
And Dragons director of rugby Robert Beale was quick to pay tribute to Burns' work ethic.
He added: "Everything Lloyd has achieved in life he has earned through hard work and dedication, his enforced retirement from the game has come as a massive shock to Lloyd and his family and will resonate throughout the rugby world.
"I am personally relieved that this serious condition has been identified off the field of play and would therefore like to thank our medical team at the Dragons, staff at the Royal Gwent Hospital and University of Wales Cardiff for all their efforts in ensuring Lloyd has and will continue to receive the highest standards of care."