When operations become safer, attention inevitably shifts from mortality to morbidity. Unfortunately, morbidity is more difficult to measure than death, but it is arguably of greater interest to the patient and to those from public or private institutions that have the responsibility for balancing a health care budget. Studies that focus on morbidity are currently few, and specific risk models are being developed. It is already evident that risk factors associated with hospital death are qualitatively different from risk factors associated with prolonged hospital stay. The study of morbidity after coronary artery surgery is important to surgeons and physicians, to assess quality of care and the impact of new treatments and procedures.