The main purpose of any Cardio Machine is to raise your heart rate. With the best cardio exercises you are not twiddling your thumbs, you are moving the large muscles in your body which require a lot of oxygen which is circulated in your blood. When you get your blood pumping, your heart rate rises to pump the blood to your working muscles. If you are out of shape and look to get back into it, your extremities may fatigue before your heart does. If you have the knowledge about which cardio machines are best for your goals, you can maximize your cardiovascular exercise.