Selected items of medical history, physical and laboratory findings, diagnoses, and treatment methods in 770 patients were stored by computer to assess utilization and effectiveness of medical care in a cardiac care unit. Utilization was expressed in terms of the distribution of final diagnoses and selected, cardiac complications in addition to occupancy rate. Effectiveness was expressed in terms of incidence and location of deaths from theoretically preventable causes, and in terms of resuscitation results, in addition to mortality in acute myocardial infarction. The same data permitted a study of prognostic factors in acute myocardial infarction. Excess mortality was associated with diabetes, previous heart failure, and age of 65 years or greater. Systematic collection of routinely available clinical information permits studies of hospital operations and of specific diseases, provided basic assumptions about objectives of care are acceptable.