Heart Disease Killed Disney Star Michael Galeota

Disney star Michael Galeota's history of high blood pressure led to heart disease at just 31 ... this according to the death certificate.

The

-- obtained by TMZ -- shows the actor's cause of death was atherosclerosis heart disease ... a build-up of plaque that clogs the artery wall. Hypertension is also listed as a significant factor.

TMZ broke the story ... Michael died back in January and was discovered lying unconscious in his living room. He'd been battling high cholesterol and diverticulitis -- inflammation of the digestive tract.

The death certificate confirms the star of "The Jersey" on the Disney Channel died of natural causes.