DUBLIN (AFP) - Ulster and Ireland prop Simon Best announced Monday his retirement from professional rugby union as a result of the heart problem that cut short his participation at last year's World Cup.

He was taken ill after making three appearances during Ireland's ill-fated World Cup campaign in France with an irregular heart rhythm.

While his condition has not been attributed to playing rugby, Best's medical experts have advised him against resuming the intense levels of training and playing required to participate in the professional game.

"It is with great sadness that I am forced to retire from the game at this stage in my career," Best said in a Irish Rugby Football Union (IRFU) statement issued here Monday.

"However, I have no regrets and feel immensely proud and privileged to have represented both Ulster and Ireland for the past nine years.

"I am grateful to have had the opportunity to work with coaches, management and players that I have had the utmost respect for and have formed lifelong friendships with many."

He added: "I would like to thank the Ulster and Ireland supporters and my friends and family for their loyalty and support throughout my career and during this difficult time.

"I would also like to take this opportunity to thank the IRFU and their medical team for the extremely high standard of care that I have received.

"Finally, having grown up as a supporter of Ulster and Irish rugby, I would like to wish the players and management of both squads all the very best for the rest of the season and the coming years."

Ireland coach Eddie O'Sullivan, paying tribute to Best, said: "Simon has been an integral member of the Ireland squad since he won his first cap in 2003. He was an incredibly honest, talented and hard working player in every aspect of his participation in the game and a model professional.

"In addition to that, he was and still is an extremely popular guy with all the players and it is very unfortunate that his career has been cut short by this condition when he still had so much more to offer Irish rugby.

"I would like to wish Simon and his family the best of luck for the future."

Best, who turned 30 earlier this month, made his Ireland debut in 2003 and won 23 caps for his country, including two as captain, and scored one Test try.

He began his professional career with Newcastle in 1996 while still a student in the north-east English city, and three years later joined his native Ulster, for whom he made 124 appearances and captained to the Magners (Celtic) League title in the 2005/06 season.

He is also the elder brother of Test hooker Rory Best, who came off the bench during Ireland's 34-13 Six Nations victory over Scotland at Croke Park here on Saturday.