Hundreds of spectators watched as a woman was "dramatically" thrown from her horse while playing polo.
Catherine Yates, 20, of Pershore, Worcs, was playing in Cirencester, Gloucestershire, when she collided with two other players, an inquest heard.
Witnesses saw the horse roll over the experienced player after her saddle broke. She died later in hospital.
Recording a verdict of misadventure the coroner said no criticism could be levelled at anyone for her death.
Miss Yates, who was competing against the Northern Ireland polo team for North Cotswolds, was airlifted unconscious to Frenchay Hospital, near Bristol.
Six days later, on 9 August 2006, she died from a reaction to a sedative administered to treat her brain injuries.
At the inquest in Flax Bourton Village Hall, near Bristol, a statement was read from Miss Yates' father Ian, from Pershore, who witnessed the accident along with his wife Wendy.
He said: "We have one question. While in the ITU [Intensive Therapy Unit], my daughter was treated with a number of drugs to reduce the swelling in the brain.
"According to the consultant that treated her and the post-mortem examination it was likely that one of these drugs caused muscle damage which caused her heart to stop pumping normally and ultimately led to her death.
"There have apparently been a small number of similar cases before and we wondered if there are lessons that can be learnt from this?"
Medical experts told the court Miss Yates ultimately died from a combination of severe brain injuries and Propofol Infusion Syndrome, a rare reaction to the anaesthetic Propofol.
Delivering his verdict, Avon deputy coroner Brian Whitehouse said he accepted the medical cause of death as severe head injuries and Propofol Infusion Syndrome
"From the evidence I've heard today [Wednesday], I don't think any criticism could be levelled at anyone, bearing in mind the probably unsurvivable head injury."
Miss Yates, who was a member of the Croome Hunt Pony Club branch in Worcestershire, had recently graduated with a first in natural sciences and was due to start a post-graduate course at Cambridge in October 2006.