A Swedish man has died during surgery to increase the size of his penis, in the first case reported in the world.

The otherwise healthy 30-year-old was undergoing an operation to elongate and enlarge his penis using fat cells taken from his torso and injected into his member.

As the surgeons were about to complete the injection, the patient's heart rate increased and his blood pressure dropped, causing a heart attack.

It was concluded the patient died of a lung embolism, after fat loosened during the surgery traveled in veins cut during the surgery up to his lungs.

"This is the first described case where a seemingly simple and safe procedure of penis enlargement by autologous fat transfer caused sudden death in a healthy young man," authors of the case study reported in the Journal of Forensic Sciences.

The surgery was risky as the man had the penis elongation procedure shortly before the girth-increasing fat injections

Some of the fat meant to increase the girth of his penis leaked into his veins punctured during the first procedure.

"We suggest that the risk of fat embolisation might be higher when pretraumatised tissue is subjected to fat injection, like in this case, where a penis elongation was performed before the fat injection," the report authors concluded.

Studies have shown the procedure of injecting fat into the penis can disfigure men – leaving them with scarring and infection, according to the NHS.