My stepmom's vet told her that her cat was bitten by a mosquito that had bitten a dog with heartworms. The scary part about that
-- her cats are all inside cats so that means it was a mosquito that got into the house. The vet told her that he could treat the symptoms only.

Oh yeah, before I forget, I wanted to mention that my stepmom originally thought Lucky was just having a lot of hairballs and finally took him to the vet when it seemed to be excessive. So, don't overlook this symptom if it happens to your kitty.

I appreciate everyone's kind advice and good wishes. You are all the best!