Best-selling author and philanthropist Greg Mortenson has canceled a May 3 speaking engagement in Massachusetts, citing health concerns.

Mortenson, whose Pentagon-celebrated non-fiction book "Three Cups of Tea: One Man's Mission to Promote Peace -- One School at a Time" is under scrutiny for its veracity, was scheduled to speak at an event organized by the Massachusetts Conference of the United Church of Christ.

A spokesman for the group told the Worcester Telegram & Gazette Mortenson is having surgery to repair a hole in his heart.

Mortenson is co-founder of the Central Asia Institute, which has helped establish and support about 180 schools in Afghanistan and Pakistan.

Recently, however, CBS' "60 Minutes" ran a segment questioning the true scope of Mortenson's work, pointing out some of the schools he is credited with establishing do not exist.

Mortenson fired back in an e-mail, calling the allegations "a distorted picture using untrue information.''