The man was descending from the Sidelenhütte mountain hut in the canton of Uri when he went into cardiac arrest.
The hiker happened to be on the phone at the time and when the person at the other end of the line noticed he was having difficulty breathing and appeared confused, the Rega was contacted.
Rega rescue workers were initially unable to contact the hiker but the second time they called, a young woman answered the phone.
She said that she and her partner had come across the man who was in a seriously weakened condition, the Rega said in a statement.
Thanks to the service's mobile phone app, the air rescue service was able to determine the exact location of the man. A helicopter was sent to the site.
However, during the telephone conversation between the Rega and the woman, the older hiker lost consciousness.
Aware that every moment counts in such situations, rescue workers then instructed the woman how to carry out emergency CPR over the phone.
Shortly afterwards, the Rega helicopter arrived and the man was transported to hospital in a stable condition.