Wales hooker Lloyd Burns has been forced to retire from rugby with immediate effect.
The Newport Gwent Dragons forward, who has won seven caps and was part of Wales' World Cup squad in New Zealand last autumn, has been sidelined since January due to a neck injury.
But the Dragons have now revealed that "ongoing tests" have revealed aorta damage, with possible heart surgery to follow.
Burns, 27, made his Wales debut against the Barbarians in Cardiff last June, going on as a second-half replacement for Huw Bennett.
At the time, he was dual-registered with the Dragons and this season's British and Irish Cup finalists Cross Keys.
Dragons director of rugby Robert Beale paid tribute to Burns, and said his enforced retirement had come as "a massive shock".
Beale said: "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. I would therefore like to thank our medical team at the Dragons, staff at the Royal Gwent Hospital in Newport and University of Wales, Cardiff for all their efforts in ensuring Lloyd has, and will continue to receive, the highest standards of care."
Burns first featured for the Dragons during the 2008/09 season, having played for Pontypool and Cross Keys, but injury meant he could play no part in this season's RBS 6 Nations Championship when Wales won the title and clinched a Grand Slam.
Burns went to the World Cup as one of three hookers in Wales coach Warren Gatland's squad, featuring alongside Bennett and Ken Owens.
Burns, who worked as a builder before moving full-time into rugby, made four appearances during the World Cup.
He started the 81-7 victory over Namibia in New Plymouth, and appeared as a replacement in the pool games against Samoa and Fiji, scoring a try when Fiji were routed 66-0.
What proved to be his final cap came in the bronze medal match against Australia in Auckland, a game that Wales lost 21-18.
He was subsequently advised to take a minimum three-month break from rugby after a neck problem surfaced, which ended his Six Nations hopes this season.
Ireland prop Simon Best, brother of current Ulster and Ireland player Rory, was forced to retire in 2007 due to a heart problem that emerged during Ireland's preparations for the Rugby World Cup in France that year.