Heavy D -- Cause of Death Revealed

Heavy D died from a pulmonary embolism caused by deep leg vein thrombosis ... and a long flight back to L.A. from a Michael Jackson memorial concert may have been a contributing factor.

A pulmonary embolism is a blockage of one or more arteries in the lungs -- most often caused by blood clots which travel in from other parts of he body. In Heavy's case, the clot was formed in his legs.

Days before Heavy died, he was on a flight back from Europe, after performing at the Michael Jackson tribute concert in Wales.

Officials from the L.A. County Coroner's Office say Heavy also suffered from heart disease, which could have been a contributing factor in his death.

The Coroner's Office has classified the death as "natural."

As TMZ first reported, Heavy died on November 8, 2011. He was 44 years old.

Deep leg vein thrombosis is often associated with long plane flights, in which a clot can form due to prolonged immobility.

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