Country music star Johnny Cash was joking with hospital staff and doing well despite suffering some pulmonary problems after heart surgery, hospital officials in Nashville said.

Baptist Hospital spokeswoman Aileen Katcher said doctors would not release more specific information about Cash's setback early in the weekend."The only thing more I can say is that he had problems with his lungs," she said Tuesday. "The doctor says it doesn't happen to all (bypass) patients, but it's not unusual."

Cash, 56, remained in intensive care following double-bypass surgery Dec. 19.

"He is up and walking around. He's doing well," said another hospital spokeswoman, Debbie Koch. "He was joking with hospital staff and seemed in good spirits."

Cash, known for such songs as "A Boy Named Sue" and "I Walk the Line," was expected to remain hospitalized through the week, doctors said.