You have some options depending on what you would like to do.
Cat's with heart conditions, depending on the severity, actually need more attention paid to their teeth. Oral infections can complicate heart disease by leading to infection of heart valves, and can also contribute to frequent urinary tract infections. In addition, it's painful, which may be part of his restlessness.
If possible, if you can have him evaluated by a cardiologist, they can perform an echocardiogram on the heart to see if he would be a candidate for anesthesia and a dental cleaning. This can also be done by a specialist, and while it will cost more, you can even have a boarded anesthesiologist monitor anesthesia. If he hasn't had an ECG and blood pressure, at a minimum, these should be performed by your vet. Your cat may need oral infections drained or teeth extracted.
With older cats with urinary tract infections, it's very important to perform a urine CULTURE as well as a urinalysis at the end of treatment, and then 2-4 weeks after to make sure it hasn't returned. Again, with his teeth, I'm concerned he may have recurrent issues.
Did they check his thyroid? Double check with them that it was normal if you aren't sure. Hyperthryoidism can lead to heart disease and behavioral changes.
Possibilities for him at this point for the vocalization are pain (teeth, arthritis, other), underlying disease, such as hyperthyroidism
, or dementia, or unlikely but possible - brain tumor.
Once you have gone as far as you can/will medically, I would recommend pulse antibiotic therapy for his teeth and trying a round of pain medicine to see if it helps him settle. I would recommend buprenex under the tongue/in the cheek.
If that doesn't help, then you could look into medication for anxiety/dementia. Some of the medications can be compounded into a transdermal form that can be rubbed on his ears
, minimizing his and your stress.
I know this was a long post. Please let me know if you have questions or need anything else. I'm here, and want to help. :)