Well, that depends on many things, including the genetic makeup of the patient, the skill of the surgeon, the types of grafts used (arterial vs. venous) and a good helping of dumb luck. In general, the arterial grafts (generally the left internal mammary artery, abbreviated LIMA and the right abbreviated RIMA) will last a lifetime, however, saphenous vein grafts will often close after 5 years or so. However, even if a graft closes, often a new operation will not be necessary if the body has formed an alternate network of blood vessels (called collateral vessels) in the meantime.