Shareef O'Neal is currently undergoing heart surgery to correct an irregularity that forced the UCLA basketball star to miss the 2018 season ... TMZ Sports has learned.
We broke the story ... Shaq's 18-year-old son -- one of the top college freshmen in the country -- learned about his medical condition during a routine checkup with team doctors earlier this year.
At the time, Reef told us, "Thank God the UCLA medical staff caught it early."
On Thursday morning, Shareef went under the knife -- and his mother Shaunie was there to see him off.