Dog makes the stunning revelation on an upcoming episode of "The Dr. Oz Show" ... revealing he's been diagnosed with a pulmonary embolism.

In the clip, Dr. Oz tells Dog he's a "ticking time bomb" before offering this sobering message ... "You're not going to be here with the heart the way it is right now."

Dog says he learned of the scary diagnosis after he was rushed to the hospital a week and a half ago with chest pains.

It's not totally bleak for Dog ... he says he's on the road to recovery.

We broke the story ... Dog's family wanted him to make major lifestyle changes after the heart scare, and it seems like he heard their message loud and clear.

Dog, who is on blood thinners, says he's eating healthier and working to kick his smoking habit.