Further tests will be carried out concerning the deaths of two soldiers during SAS selection training in the Brecon Beacons.
Edward John Maher and Lance Corporal Craig John Roberts collapsed on one of the hottest days of the year while climbing south Wales' highest mountain. A military colleague of theirs remains in a serious condition.
Witnesses on the day said they saw two soldiers "clearly in distress" who pleaded with them for some drinking water.
An inquest at Brecon Law Courts in Powys, mid Wales, gave the medical deaths of the pair as "unascertained".
Speaking at the brief hearing was Dyfed Powys Police Detective Inspector Ieuan Wyn Jones.
He said that L/Cpl Roberts had been pronounced dead on the mountain at 5.15pm, while Mr Maher died at Prince Charles Hospital in Merthyr Tydfil almost three hours later.
"Post-mortems have been carried out and the causes of death are unascertained," he added.
"Further investigations are being carried out."
Mr Maher and L/Cpl Roberts were understood to be taking part in the aptitude training element of the course to become SAS reservists.
They were climbing Pen Y Fan, the highest mountain in southern Britain, on July 13. It is known as the location for the "Fan Dance" where soldiers hoping to join the special forces march over the mountain carrying a heavy pack and a rifle, then do the route in reverse in a set time.