How to improve my cardio vascular endurance?

Exercise!: The only way to improve one's cardiorespiratory endurance or aerobic condition is via (more) exercise. Of course, if you've already been exercising and gradually pushing yourself w/o improvement, you should go see your family physician to make sure you don't have a heart or lung condition preventing you from getting better.

Aerobic conditioning: After an initial health care provider's evaluation to "rule out" any contraindications to vigorous exercise, progressively increasing and consistently performed, aerobic training will strengthen your heart (for its oxygen pumping function) and your lungs (for its . Efficiency in "taking up" oxygen). This would be a great start!