Redskins' coach Joe Gibbs underwent an operation several weeks ago to unclog an artery to his heart. Gibbs, a 64-year-old diabetic, said the procedure ``has no effect on my work, or my tenure with the Redskins.'' He said Wednesday he had the precautionary procedure in mid-April at a Washington hospital on the advice of doctors. A small tube, known as a stent, was placed in the artery. Gibbs said he has never had a problem with his heart, and the blockage was discovered during a routine physical. ``I suffered no ill effects prior to the procedure, and have had none since,'' he said.