Clinical conditions such as beta-blockade, cardiac conduction defects, use of a cardiac pacemaker, and cardiac transplantation preclude use of heart rate to regulate the intensity of prescribed exercise. Purpose: To evaluate the suggestion that Borg's RPE may provide a valid alternative, and to weigh possible alternatives. Methods: A brief review of factors modifying RPE, and an analysis of RPE data obtained in patients following cardiac transplantation. Results: Many factors modify an

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... l's perceptions of effort, and in consequence simply exercising to a fixed RPE can result in either too low an intensity to induce the required training, or a dangerously high intensity of exercise. Conclusions: RPE does not provide a safe method of regulating exercise after cardiac transplantation. A better alternative is to establish the individual's oxygen cost of walking, and to prescribe a set walking distance to be covered in a set time, reserving the RPE for a fine-tuning of this prescription