The ESPN tennis announcer who was fired after using the word "guerilla" during a Venus Williams match has suffered a heart attack ... and claims it was brought on by the stress surrounding the incident.

Doug Adler spoke with Clay Travis from "Outkick The Coverage" and said he was rushed to a hospital Tuesday and is still there today.

Adler says his doctors are largely blaming the heart attack on stress -- and Adler says it's because he was branded a racist by people who incorrectly believe he was referring to Williams as a "gorilla" during the Australian Open.

Travis mentions that Adler had previous heart conditions.

As we previously reported, Adler is suing ESPN for wrongful termination. He previously told TMZ Sports he's "anything but a racist."