A COCKTAIL of drugs, including cocaine, has been found as the secondary cause of death of surfing legend Andy Irons, but a  forensic pathologist hired by the family has disputed the finding.

Irons, a three-time world champion, died on November 3 while travelling with the Association of Surfing Professionals World Tour.

The official autopsy report, from the Tarrant County District Attorney's Office in Forth Worth, Texas, has revealed sudden cardiac arrest as the cause of death due to a blockage of the main artery of the heart.

Although the condition only usually affects those older than 40, the autopsy reveals the 32-year-old had a genetic weakness to the disease with both his grandmother and grand uncle dying of heart failure.

The report also lists a second cause of death as acute mixed drug ingestion revealing traces of xanax, used to treat anxiety, methadone, used as treatment for chronic pain, cocaine and methamphetamine were present in his blood at the time of his death.

In a prepared statement, the Irons family have revealed Mr Irons suffered from bipolar disorder, diagnosed at age 18, adding he often used illicit drugs to calm severe mood swings.

"Andy seemed to feel bullet-proof," the statement read.

"Andy was in some denial about the severity of his chemical imbalance and tended to blame his mood swings on himself and his own weaknesses, choosing to self-medicate with recreational drugs.

"But travelling while sick and suffering from an undiagnosed heart condition was more than even Andy could overcome.

"We are hoping that people will remember Andy for his very full life, which included his intense passion for surfing and the ocean, his astonishing achievements as a world-class athlete, and his devotion to the family and friends who love him dearly and miss him every day."

Dr. Vincent Di Maio, a prominent forensic pathologist in San Antonio, who has consulted on many high-profile cases, was asked to review and explain the autopsy results to the family.

"This is a very straightforward case. Mr Irons died of a heart attack due to focal severe coronary atherosclerosis, i.e., 'hardening of the arteries.'

"He had an atherosclerotic plaque producing 70%-80% narrowing of his anterior descending coronary artery.This is very severe narrowing. A plaque of this severity, located in the anterior descending coronary artery, is commonly associated with sudden death."

Dr Maio believed drugs should not have been listed as a secondary cause of death, because "it was not the cause of death and did not contribute to the death".