Surgeons saved a man's life after a three-week erection nearly killed him.

The businessman, 55, was forced to undergo an emergency operation after his problem firmly persisted for a staggering 21 days.

Doctors at a hospital in Kolkata, India, eventually performed the surgery to put the middle-aged man out of his misery.

But although the hour-long operation was successful, it rendered the man impotent.

"It was very late when the man sought treatment," said Dr. Avishek Mukherjee.

"The treatment has to be sought within six hours; otherwise it could even lead to death, besides the degeneration of the penis."

The man, whose name is not being revealed in order to protect his privacy, had not taken Viagra to boost his sex drive.

Doctors believe he was suffering from a condition called priapism, triggered by a nervous system disorder.

The disease prevents blood from draining out of the penis.

"During erection, the blood flow stops," Dr Mukherjee said.

"So, if the erection persists for more than an hour, the supply to the penis is reduced, which can damage the organ. If the supply remains cut off for a long time, the penis can even become gangrenous."

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