The Rated Perceived Exertion (RPE) has been used as an indicator for work intensity. An RPE of 15 or greater has been used to indicate that the anaerobic threshold has been crossed and for the termination of exercise testing in cardiac patients (ACSM, 2000). The purpose of this paper was to examine the RPE 15 ("hard") as an indicator for stopping stress test in patients with heart failure (HF) treated with beta-blockers. Five males mean age 56, range 42-68 who were diagnosed with HF (mean EF 37%, SD 4%) and were treated with beta-blockers, performed the Balke walking treadmill test. The mean peak VO2, RPE and heart rate as % of maximal predicted heart rate during the last minutes of exercise were 13.9 mL/kg/min, SD 4.5 mL/kg/min, 12.6, SD 2 and 62%, SD 4% respectively. Criteria for terminating the tests were, fall of systolic blood pressure more than 10 mmHg, ST depression, and no increase of VO2 despite an increase of workload. The preliminary results indicate that a RPE of 15 may be an overestimation of the cardiac metabolic stress experienced by cardiac patients. Therefore the use of a RPE of 15 for terminating stress test in HF patients on beta-blockers may be inappropriate.