Why is cardio so important to physical fitness?

Many reasons: Cardio exercise increases physical endurance; is good for a person's heart and blood vessels; helps prevent many conditions like diabetes, coronary heart disease, and some cancers; and can contribute to a longer life that has good quality.

Heart, Blood Vessels: Carry blood, oxygen & nutrients throughout the body for life. The heart (pump), lungs (o2 source) and vessels (pipeline) are the body's superhighway and needs to be optimized for optimal functioning. Cardio conditioning ensures the strength and integrity of this vital system.