Kitten - heavy breathing

My wee 7 week old kitten looks as if se is recovering from a long run.
Her little chest is heaving in and out, I am taking her to the vet tomorrow but would like to get your opinion on what it might be, heat perhaps?
She's eating and drinking but not bouncing about the place like usual.
This girl has had so many ups and downs, I really am trying my best for her.
Also its been month of creams and eye drops but her eye is still watering.
These little ones can be so stressful can't they.

Has she been seen by a vet before? Echo was the same way, anything strenuous would have him gasping for air, he was diagnosed with ASD (atrial septal defect). Instead of a 4 chambered heart he pretty had much only had 3 chambers, he passed away at 8 months old. Definately bring up the heavy breathing with your vet, and keep us posted.

My Persil had a breathing rate of over 80 as a kitten and was not active, and the vet diagnosed a diaphragmatic hernia, pulling all her internal organs into her chest. It can sometimes be operable - she was lucky and is now fine. An Xray shows it up at once. Good luck, I do hope it is nothing so serious.