Rating of perceived exertion (RPE) is a valuable and reliable indicator for monitoring your exercise tolerance. It is usually used as part of an organized cardiac rehab program. It is probably most useful to first learn about RPE with a health professional, such as an exercise physiologist or trainer, and then you may be able to use it when you exercise on your own.

The RPE is a means of determining how hard you are exerting yourself, including physiological (how hard you are breathing, how fast your heart is beating) and muscular strain (how much you feel the exertion in your muscles). The scale measures your answer to the question: "How hard do you feel the exercise is?" The scale goes from 6 to 20.