A study in the New England Journal of Medicine showed that one of the best tests to predict your risk for having a heart attack is your Recovery Heart Rate.
Recovery heart rate is a measure of fitness and a slow recovery from exercise means that you are out of shape. The study really shows that being out of shape increases your chances of having a heart attack.
To measure recovery heart rate, exercise on a treadmill until you breathe hard, record your heart rate, and hold that pace for at least a minute. Then cool down and measure your pulse rate exactly one minute after stopping. If your heart does not slow down at least twelve beats in the first minute, you are in poor shape and at increased risk for a heart attack. If your heart rate slows down more than fifty beats in the first minute, you are in excellent shape.
You can also use the recovery heart rate to measure improvement as you get into shape. This test can cause irregular heart beats in people with damaged hearts, so check with your physician before you try it.
Cole CR et al. Hear-rate recovery immediately after exercise as a predictor of mortality. New England Journal of Medicine 1999(October 28);341(18):1351-7.