Aerosmith has canceled its 'Let Rock Rule' tour date tonight (August 13) after an unexplained illness felled Joey Kramer. They were set to play in Concord, California.

"The band regrets not being able to perform for their fans," a message at Aerosmith's Facebook page says, before directing ticketholders to refund sites.

TMZ is reporting that heart problems are to blame. They say a member of the Aerosmith crew revealed the 63-year-old drummer will need surgery -- though that's obviously unconfirmed.

A concert set for later this week at George, Washington, has also reportedly been nixed, according to TMZ. The 'Let Rock Rule' tour, which finds the Boston legends teaming up with former Guns N' Roses guitarist Slash, is currently scheduled to continue through September.