The Slovakian rider suffered an abnormally high heart rate in a mountain bike race in Valencia at the weekend and was treated on Friday in Ancona, Italy.
Sagan retired from road cycling last year but is still focused on qualifying for the Paris Olympics in cross country.
"Hello guys, just a brief update. Everything is under control and in just a few days I'll be back on my bike," Sagan said in a post on Instagram.
A medical report from the Marche University Hospital said an internal electrophysiological study was carried out and that "a subcutaneous event recorder was implanted which will allow the future monitoring of the athlete."
Sagan had already competed in two mountain bike events this year as he seeks to earn UCI points in order to help Slovakia qualify for the competition in the Olympics.
He was scheduled to compete in the UCI World Cup events in Brazil in April.
