This video by Nicole Wilkins, Figure Champion, has some good tips on how to increase the effectiveness of a cardio day at the gym.
To expand on that, mix up your cardio and the level of intensity. For example, 20 minutes treadmill, 20 minutes elliptical and 20 minutes bike, rather than 60 minutes running at the same pace on one machine.
Even further, stagger intensity of cardio on the above machines with 2 minutes of zero incline or usual pace and 1 minute high intensity with faster speed or increased incline.
You can increase your endurance over time with effort and consistent training.
Dream Big, Work Hard!