Isaac Hayes [ tickets ], the deep-voiced soul singer best known for "Theme from Shaft," has reportedly canceled his summer tour due to a heart condition.

The 63-year-old R&B legend, who was born in Covington, TN, was due to play the Monterey Bay Blues Festival in California on June 24. According to a press release issued by the festival, however, Hayes' management team has informed festival organizers that the vocalist is following his doctor's orders and pulling the plug on the entire tour due to a heart condition.

The Monterey Herald, in an article published Friday (6/16), also confirmed that Hayes' management is canceling Hayes' entire summer tour. No further information was available at press time.

Hayes was supposed to be the Saturday headliner during the 21st annual Monterey Bay Blues Festival, a three-day event that--like the more famous Monterey Jazz Festival--is held at Monterey Fairgrounds. The search is underway to find a replacement of equal stature and festival organizers say they hope to make an announcement soon.

Hayes was one of the most influential and successful artists of the late-'60s and early '70s, known for such top-selling albums as 1969's "Hot Buttered Soul." He was inducted into the Rock and Roll Hall of Fame in 2002.

Despite his heavy music credentials, Hayes is known to many simply as the voice of the chef character in Comedy Central's animated "South Park" series.