This also means that the muscles are able to maximize the use of this oxygen delivered by the blood to power your movements. In short, your cardiovascular system is considered fit if circulation and oxygen use are efficiently done.When you have cardiovascular fitness, you are able to withstand aerobically challenging activities regardless of the duration. Improved cardio fitness also reduces your risk of acquiring and developing various diseases related to the heart and lungs since the better your circulation, the less pressure is put on these organs.