Seven months' pregnant Lesley Boden suffered an unexplained cardiac death called Sudden Adult Death Syndrome (SADS), which also killed her unborn daughter, Rosina Eleanor.
An inquest heard that the 33-year-old from West Wellow, Hampshire, had spoken to her partner Richard Wade by Skype on the evening before she was found dead, and all was well.
In a short statement Mr Wade, who is also an army major who was then based in Cyprus, told the Winchester inquest: "We talked about the baby and me coming home in a few days' time. Nothing was out of the normal. Lesley appeared happy and in good health."
The alarm was raised when work colleagues could not get hold her on May 16 and Sergeant Major Mark Watson and Lieutenant Rachel Gibbs went to her house and broke in.
Mr Watson said: "I could see Lesley Boden on the bed,' he explained. "She looked to be sleeping, her eyes were closed and she seemed peaceful. She was cold to the touch."
She had been dead for at least six hours, the hearing was told.
Pathologist Adnan Al-Badri said he could find no problems or infection in all of Ms Boden's organs and tests showed there was no alcohol or drugs in her system. The baby and its placenta were also completely normal with no signs of problems or infection.
He said: "We do not know really what she died of but the most likely cause is a sudden cardiac death and the reason for that is that we ruled out any other cause of her death.
"Although her heart looked normal that does not rule out problems with the electric conduction of the heart that can cause death.
"Sudden Adult Death Syndrome is a group of conditions that can cause sudden death in adults. They are caused by an abnormality of the rhythms of the heart."
He added that he did not believe that Ms Boden being pregnant had any effect on what happened. Recording a verdict of death by natural causes caused by sudden unexpected maternal/adult death,
Central Hampshire Coroner Grahame Short said: "It's a clearly very sad death of an apparently fit and healthy woman in the last stages of a pregnancy which makes the loss even harder because her daughter died in utero at the same time."
He explained that no underlying condition or problem had been found and added: "I realise that this is not altogether satisfactory but I have to accept that, within the limitations of medical knowledge at this time, it's not always possible to be absolutely specific."