1. Several approaches to assessment of physical work capacity in the upright posture in normal adults and cardiac patients have been reviewed critically. 2. Preliminary experience has been presented with a new multistage treadmill test of maximal exercise which permits appraisal of either a physically trained normal subject or an impaired but ambulatory cardiac patient. 3. The most effective means of differentiating cardiacs from normals has been an estimate of the total oxygen intake/Kg of body weight. 4. The need for monitoring the circulation with respect to arrhythmias, ischemia and/or hypotension has been emphasized. The authors wish to acknowledge their appreciation of many physicians, particularly Dr. Robert M. Levenson of the Seattle Cardiac Work Evaluation Clinic, and medical and graduate students who have assisted in the testing of patients and normals. The assistance of Mrs. Gladys Pettet is gratefully acknowledged also.