Lionel Richie is back in the hospital after suffering another heart issue ... forcing him and Earth, Wind & Fire to cancel their next three shows, TMZ has learned.

Sources with direct knowledge tell TMZ .... Lionel is currently hospitalized and receiving treatment for atrial fibrillation, an irregular heartbeat.

We're told doctors are treating Lionel with an AFib ablation, which is not considered a major procedure. The minimally invasive treatment creates tiny scars in the heart to block faulty electrical signals and help restore a normal rhythm.

As a result of the latest health scare, we're told the next three dates on Lionel and Earth, Wind & Fire's "Sing a Song All Night Long" tour have been canceled.

The shows were scheduled for Saturday in San Francisco, September 30 in Chicago and October 2 in Columbus, Ohio.

This marks Lionel's third hospitalization in as many months.

As TMZ previously reported, he checked himself into a St. Louis hospital after an August concert and spent several days in the ICU undergoing tests for cardiac issues.

Lionel was released and sent home after the three-day stay.

He was also rushed to a hospital in June after feeling "dizzy" and "strange" during a concert in St. Paul, cutting the performance short before paramedics took him away by ambulance.