I was hospitalized for minor heart attack and everyone at work knew because my boss told someone (who is threatened by me) and also his good buddy. This co-worker also told one our biggest client.. they now treat me less than able

I also checked out early because I was scarred of losing my job

If you are in the US and wondering about HIPAA laws regarding transmission of medical information, this gossiping around the workplace isn't what that law covers.
Handling of cases takes a long time, and 99% claims are rejected. You might have better luck with a civil lawsuit, but you need to ask for and prove damages of a specified dollar amount.

You should above all talk to company personnel or management, and it would be best to write it down. Stick to facts and dates and keep it short. Does your company have a policy handbook? That is a key question, what company policy is.

While your boss (and especially your co-worker) may have committed a breach of ethics in spreading the info, nothing illegal was done.

What is your question? You really didn't ask one.

If the attack was minor there is a chance of full recovery. I had a minor heart attack over 10 years ago. I had 2 stents put in and since then have had no indications of heart problems. You do need to see your cardiologist regularly.

Tell your customer that you got a clean bill of health.