My cat has a chest tumor and heavy breathing. Can I give her ZydaClin?

I recommend you have your cat seen by a veterinarian immediately if she is having trouble breathing/irregular breathing. She may be dealing with allergies, asthma, or even heart disease, which is often very difficult to detect in cats until it becomes an emergency situation such as this. It's better to be safe than sorry, so I recommend you have her examined by a vet right away. I do not recommend you giving 2cute the ZydaClin you have from your other cat's dental issue, as misuse of antibiotics can lead to resistant bacteria. Without further testing, there is no way to tell if what you are concerned is a tumour is due to infection, trauma or allergy, or if it is a mass. Masses can be of a malignant (cancerous) type that can spread elsewhere and/ or invade the healthy tissue around them, or a more benign (noncancerous) type that is unlikely to spread. Cancerous types of masses are less common than benign ones, but I recommend having 2cute seen by a vet to have the growth tested and to guide treatment.