Hugh Hefner Death Certificate Reveals Cardiac Arrest, Blood Infection

Hugh Hefner ultimately died of cardiac arrest, but

reveals he was also battling a few other ailments.

According to the doc, Hef was suffering from septicemia -- a severe inflammation of body tissues triggered by an infection in the blood. He'd also been dealing with E. coli ... and both are listed as contributing factors.

The main cause of death is listed as cardiac arrest.

As we reported, Hefner died last week at the Playboy Mansion ... surrounded by loved ones at 91.