An ideal heart rate is one which exercises the heart appropriately yet doesn't cause too much stress to the heart. This instruction is a method recommended by cardiologists but keep in mind everyone is different. Always inform your doctor before starting any exercise regimen.
Subtract your age in years from 220. So if you are 20 years old, you will have 200.
Multiply the answer to step one by 75%. (.75) The answer you get is the ideal heart rate you should be aspiring to have immediately following exercise. *If you are 20 and got the answer of 200 above, you multiply 200 x .75 and you will get 150 as your ideal exercising heart rate.
Count your pulse via your wrist for 15 seconds immediately after exercising and multiply by 4 to check where you are at compared to your ideal you found in step 2. Remember, you are only counting your pulse for 15 seconds.