What Causes Painful Calves During Morning?

Upon arising in the mornings or after a nap occasionally. the calves of both legs are extremely painful, difficult to walk. I recently had two stents in lower arteries and that seemed to help for a while. However, the condition has returned, although not quite as severe. I have a check up scheduled with the cardiovascular surgeon #/18, but am hoping to get some clues prior to that exam. Thank you.