In 1981, the NHLBI offered a special competition for the evaluation of cardiac function in sickle cell disease patients who were enrolled in the cooperative study of sickle cell disease. The original general study protocol required assessment of the lungs, spleen, kidneys, eyes, and liver but not the heart. The cardiac function study objectives were: to determine cardiac function in a cross-section of sickle cell patients participating in the larger study; to determine the incidence, prevalence, and onset of cardiac impairment; and to assess changes in cardiac function and correlate the observed changes with other clinical data. A total of 300 patients had an entry cardiac evaluation in the third year of the study (June 1, 1981 through November 30, 1981) and an exit cardiac evaluation two years later in the fifth year of the study which was conducted at four centers.