'Rowdy' Roddy Piper -- Cause of Death ... Heart Attack From Blood Clot

TMZ has learned that "Rowdy" Roddy Piper died from a blood clot in his lungs.<br />TMZ obtained a copy of the death certificate, which shows the wrestling legend had pulmonary embolism (a blood clot) that triggered a heart attack.<br />The death certificate helps explain the clot ... Roddy suffered from hypertension for years, resulting in chronic high blood pressure. Clotting can occur as a result of high blood pressure.<br />And the document reminds everyone how much of a force Roddy was in his profession ... his occupation is listed as "PROFESSIONAL WRESTLER ... 45 YEARS."