Actor James Darren, known for his work on films including Gidget and TV shows such as T.J. Hooker and Star Trek: Deep Space Nine, has died at the age of 88.

TMZ report that the veteran performer passed away in his sleep at Cedars-Sinai Hospital in Los Angeles on Monday.

Darren’s cause of death remains unknown a the time of writing, but the actor’s son, Jim Moret, reportedly told TMZ that his father was having heart issues and was a patient at Cedars-Sinai’ cardiac unit.

It’s believed that Darren had initially gone to hospital for an aortic valve replacement, only to be judged too weak to safely undergo the procedure.