Op for bluegrass pioneer Stanley

Ralph Stanley still performs with the Clinch Mountain Boys

Bluegrass pioneer Ralph Stanley, one half of the Stanley Brothers, has undergone triple heart bypass surgery.

The 78-year-old singer and banjo player had the operation on Monday on advice from doctors after a routine check-up.

"It went as planned and everything seems to be going well," publicist Norma Morris said.

With brother Carter, Ralph was part of one of biggest bluegrass bands in the genre's early days in the 1940s, with their band the Clinch Mountain Boys.

After Carter died in 1966, Ralph continued to perform with their band. His son Ralph Stanley II is a member of the group.

His career was boosted with the 2000 release of the movie Oh Brother, Where Art Thou - starring George Clooney - which featured a number of his songs on the soundtrack.

The soundtrack won a Grammy award and was number one in the album charts in the US.