If I had known (that) your dog "is / was" agressive...

Hello Alan, Mister Micawber, Beeesneees, Mordant, Esl_Expert and other native English speakers,

If I had known (that) your dog [color=green]is / [color=red]was agressive, I wouldn’t have offered to feed it. (noun clause – existing truth – The dog was agressive then and still is now.)

The parenthetical explanation isn’t clear to me. Are [color=green]is and [color=red]was interchangeable in this sentence?

tofu may i know what is your degree in English?

Thank you, B.