Describe how being fit can help your cardiovascular system?

There are four basic elements of physical fitness:
cardiovascular endurance, muscular strength, muscular endurance, and flexibility. Each
can be measurably improved with regular exercise. But keep in mind that exercising to
build fitness is not the same thing as working out to improve athletic performance. To
be truly fit, you should develop all four elements, not just one or
two.

While each element is a part of being fit, the most
vital is cardiovascular endurance. Physiologically, cardiovascular endurance is the
sustained ability of the heart, blood vessels, and blood to carry oxygen to the cells,
the ability of the cells to process oxygen, and the ability of the blood, once again, to
carry away waste products. Since every cell in the body requires oxygen to function,
there is no more basic element of fitness than this - to see that the heart, lungs, and
circulatory system do their job.

Cardiovascular endurance is built up
through exercises that enhance the body's ability to deliver even larger amounts of
oxygen to working muscles. To achieve this, the exercise must utilize the large muscle
groups (such as those in the legs) and, most importantly, it must be sustained. With
regular aerobic exercise, your heart will eventually be able to pump more blood and thus
deliver more oxygen with greater efficiency. Moreover, your muscles will develop a
greater capacity to use this oxygen. This is part of what is called the aerobic
"training effect." Because your heart is stronger, it can pump more blood per beat, and
as a result your heart rate, both at rest and during exertions, will decrease. Your
heart will also acquire the ability to recover from the stress of exercise more
quickly.