Alvis Edgar "Buck" Owens Jr. (August 12, 1929 - March 25, 2006) was an American musician, singer, songwriter and band leader who had 21 No. 1 hits on the Billboard country music charts with his band the Buckaroos. They pioneered what came to be called the Bakersfield sound, a reference to Bakersfield, California, the city Owens called home and from which he drew inspiration for what he preferred to call American music. While Owens originally used fiddle and retained pedal steel guitar into the 1970s, his sound on records and onstage was always more stripped-down and elemental. His signature style was based on simple storylines, infectious choruses, a twangy electric guitar, an insistent rhythm supplied by a drum track placed forward in the mix, and high two-part harmonies featuring Owens and his guitarist Don Rich.

Buck Owens died in his sleep of an apparent heart attack on March 25, 2006, only hours after performing at his Crystal Palace restaurant, club and museum in Bakersfield. He had successfully recovered from oral cancer in the early 1990s, but had additional health problems near the end of the 1990s and the early 2000s, including pneumonia and a minor stroke suffered in 2004. These health problems had forced him to curtail his regular weekly performances with the Buckaroos at his Crystal Palace.  The Los Angeles Times interviewed longtime Owens spokesman (and Buckaroos keyboard player) Jim Shaw, who said Owens "had come to the club early and had a chicken fried steak dinner and bragged that it's his favorite meal." Afterward, Owens told band members that he wasn't feeling well and was going to skip that night's performance. Shaw said a group of fans introduced themselves while Owens was preparing to drive home; when they told him that they had traveled from Oregon to hear him perform, Owens changed his mind and took the stage anyway.  Shaw recalled Owens telling the audience, "If somebody's come all that way, I'm gonna do the show and give it my best shot. I might groan and squeak, but I'll see what I can do." Shaw added, "So, he had his favorite meal, played a show and died in his sleep. We thought, that's not too bad."  The front of the mausoleum where Owens is buried is inscribed "The Buck Owens Family" with the words "Buck's Place" beneath.

Answer the following question by taking a quote from the article: How did he die?
Buck Owens died in his sleep of an apparent heart attack