The man, who comes from Romandie and had completed less than a week of his military service, collapsed shortly after returning from an eight-kilometre walk on Friday, online news site Le Matin reported.
“He said that the exercises he had to do all week had exhausted him, that he could not do any more and that he was thinking about stopping,” an anonymous witness told the website.
Colleagues said that they had heard him gasping in pain shortly before the collapse.
Rega, the Swiss helicopter rescue service, arrived at the barracks in Bière, canton Vaud, just after midnight, 16 minutes after the call was made.
The man was flown to the Central University Hospital of Vaud. As he was receiving surgery, the recruit suffered a second arrest and was then placed in an induced coma by the medical staff.
This is the second time in as many years that a young man has suffered cardiac arrest after completing military training. Last year a 19-year-old died from a heart attack after his first month of training, also at Bières.
Zurich cardiologist René Schläpfer wants the army to do more to detect heart problems at the point of enrolment, the website reported.
Counselling is being offered to those who witnessed the collapse.