Daphne from 'Scooby-Doo' Death Certificate Died from Cardiac Arrest

12/21/2017 11:03 AM PST

'Scooby-Doo' Voice Actor Heather North Died of Cardiac Arrest

EXCLUSIVE

Heather North -- the longtime voice of Daphne on 'Scooby-Doo' -- died of a heart attack brought on by respiratory disease ... TMZ has learned.

North's official cause of death is listed as cardiopulmonary arrest with an underlying cause of constrictive bronchiolitis ... according to the death certificate. She also had a very low level of oxygen in her blood when she died on November 29.

As we reported ... the actress passed away at her home in Studio City following a long illness.

Heather starred on 'Scooby' for more than 30 years, and also had on-camera roles on "Days of Our Lives," "The Barefoot Executive," "Mr. Novak," and "The Fugitive."

She was 71.