7. Bad Breath: Geriatric pets are not the only ones who can suffer from dental diseases. Even in kittens as young as four months old, severe dental disease can be present as a result of common viruses and severe pain, even exposed nerves, can evolve quickly. If your pet has foul breath, don't play games with over-the-counter breath freshening tools. First, see your vet to find out if your pet has abscesses, broken teeth, gingival complications or other oral health conditions that could be causing pain and opening the window to additional disease of major organs including the heart.