The inquest heard Mr Hamlyn died from acute cardiac arrhythmia.
The inquest heard Mr Hamlyn died from acute cardiac arrhythmia.
A UK graduate died after performing an underwater "party trick" at his brother's 21st birthday, an inquest has heard.
The 24-year-old Cambridge student, Dominic Hamlyn, became unresponsive while swimming in a pool at his family home in Kent, England's southeast last year in July.
The "fit and healthy" man swamtwo-and-a-half laps while holding his breath before he stopped moving.
He was taken to William Harvey Hospital where he died later that evening.
During the inquest last Thursday (local time), his neurosurgeon father Peter Hamlyn confirmed his son had often done the underwater challenge.
Coroner Scott Matthewson said the graduate had a pre-existing heart condition and died from acute cardiac arrhythmia - known as "sudden adult death syndrome".
"Nobody could have, or will ever with any certainty, say what the medical cause was in Dominic's death," he added.
His parents wept and held each other's hands as the assistant coroner gave his ruling, which acknowledged the differences in medical opinion.
Dominic Hamlyn, 24, died after holding his breath underwater at a birthday party. He's pictured here with his mother Geraldine Hamlyn.
Hamlyn's father described his son as a "beautiful, beautiful boy".
"Why did he die?" he said.
"He was a superb athlete competing in both rugby and rowing at Cambridge. We are broken. If Dominic is to be remembered, it is as a hero and one of the world's helpers."
The family later issued a family statement, saying data showed at least 12 young people die of cardiac arrest each week in the UK, but their inquest experience suggested this was likely to be a gross underestimate.
"As a result, victim's families will continue to go unscreened and readily treatable warning signs missed," he said.
"If I were not a doctor and one with specialist expertise in sports medicine my family would number amongst them.
"In life, Dominic gave so much to others. It is up to us to ensure his legacy is not just a family immersed in our grief but that his loss brings awareness and change.
