There are many reasons for your eyes feeling heave and tired such as using your eyes too much, or prolonged computer use. The light reflecting from the computer screen will cause tried eye, blurry vision and try eyes.
Dry eyes or eye allergies can also cause the eyes to feel heavy. This may be treated with eye drops. Finally there is a condition called blepharospasm, in which there are uncontrollable spasms of the eyelids forcing intermittent eyelid closure. This condition may be treated with Botulinum toxin injections.
Given that the differential diagnosis of heavy eyes is so broad, an examination with an ophthalmologist to determine the individual nature of the heaviness is recommended. Your doctor will be able to guide you to recommendations for improvement