Functional capacity is an integral component of the pre-operative evaluation of the cardiac patient for non-cardiac surgery. Stair climbing capacity has peri-operative prognostic importance. It may predict survival after lung resection and complications after major non-cardiac surgery. However, stair climbing cannot determine the aerobic metabolic capacity necessary to survive the peri-operative stress response. The potential benefits and current limitations of cardiopulmonary exercise testing to determine peri-operative aerobic capacity are discussed. Principles for the selection of an appropriate screening test of aerobic function are put forward.