Cardiovascular system health and strength is extremely important when it comes to preventing chronic health problems such as heart attacks, strokes, clogged arteries, COPD, congestive heart failure, and diabetes. To optimally improve your cardiovascular health, you need to get your heart rate up by exercising. Target heart rate is basically your cardiovascular training intensity level. Just like weight lifting intensity, your target heart rate is a percentage of an estimated max. To find your target heart rate you start by simply subtracting your age from 220. This will give you an age-predicted max heart rate estimate. From there you can multiply the estimated max by any given intensity level to find your target heart rate. Typically you would like a training zone with a range of about 10%. The level of intensity in which you need to training is determined by your goals. A great starting goal would be to train about 70% for your target heart rate. You can measure your heart rate with a heart rate monitor, or by taking your pulse for 6 seconds and multiplying the number of beats by 10.
Example for 40 yr. old whose target heart rate training zone is 70-80%:
220 - 40 = 180 beats per minute
180 bpm X .70 = 126 bpm
180 bpm X .80 = 144 bpm