To assess medical impairments, the AMA Guides to the Evaluation of Permanent Impairment (AMA Guides) divides cardiovascular diseases into the following eight groups, each of which has its own grid: valvular heart disease; coronary artery disease; cardiomyopathies, pericardial heart disease, dysrhythmias, hypertensive cardiovascular disease, vascular diseases affecting the extremities, and diseases of the pulmonary artery. An accompanying table shows the criteria for rating permanent impairment due to valvular heart disease. Within the grids, the rows are divided into three main impairment variables: history, physical findings, and objective test results. The latter are essential in assigning cardiovascular impairment ratings. The AMA Guides names the objective test results variable as the key factor to underscore its role in assigning the impairment class in the cardiovascular chapter. For cardiovascular impairments, objective test results are always used to place the injury in its impairment class; therefore, objective test results are never used to modify the rating once the evaluator chooses the impairment class. Not all internal medicine chapters designate objective test results as the key factor, but all use one key factor that is clearly indicated in a footnote and one or two non-key factors. This rating scheme emphasizes objective test results, history, and physical findings and avoids incorporating variables twice.