The total time of the Bruce Protocol test depends on how your heart responds to it. There are seven stages and each one lasts for three minutes, according to Harvard Health. If you make it to the last stage, the test will last 21 minutes, but then there’s typically a cool-down period where you walk at a slower pace for a few minutes to bring your heart rate down. After this cool-down period, you may need to stand or sit for another 15 minutes to allow your heart rate to return to its resting state. Depending on how you respond to it, the test may be shorter for you. It ends when your heart is working to 85% of its maximum predicted heart rate (MPHR), so if that happens in the third stage, the active part of the test may only last nine minutes or so.