2:12 PM PT -- Ric's family says he was home recuperating from an unspecified surgery when he unexpectedly, but peacefully, died in his sleep.
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His wife, Paulina, says she discovered he had passed when she went to bring him his Sunday morning coffee.
Ric Ocasek's cause of death has been revealed -- The Cars frontman died of heart disease.
According to NYC's Chief Medical Examiner ... Ocasek died of hypertensive and atherosclerotic cardiovascular disease. In layman's terms, that means he had heart disease caused by high blood pressure.
Pulmonary emphysema is also listed as a contributing condition to his death, and law enforcement sources tell us he had a history of cancer. His manner of death is listed as natural.
As we reported ... The Cars lead singer was discovered unresponsive Sunday at his townhouse in NYC and pronounced dead at the scene. He was reportedly found in his bed by his estranged wife, Paulina Porizkova.
Ocasek started the band in the '70s and they busted through to stardom with their 1978 song, "Just What I Needed." They went on to have a number of hits, including "My Best Friend's Girl," "Good Times Roll," "Bye Bye Love," "Let's Go," "Shake It Up" and their biggest hit ... "Drive."
Ric was known for his distinct voice and became known as a new wave rock pioneer.