The 29-year-old Scotland international underwent a planned ablation procedure at Manchester's Spire Hospital in September after being diagnosed with a mild, benign heart arrhythmia.
McTominay has since completed further medical tests, which confirmed that he can safely resume sporting activity.
Napoli said he has now returned to full training with his team-mates after initially working separately during his recovery.
"Scott McTominay underwent further diagnostic tests, which showed that he is fit to play," Napoli said in a statement.
"The Napoli player therefore resumed training with the rest of the team after the period spent training separately."
McTominay has not played since August 30 and missed Napoli's 3-2 Serie A defeat by Inter Milan, as well as their Champions League defeat against Arsenal.
His return is a boost for Massimiliano Allegri, who can now consider the Scotland midfielder for Napoli's Serie A meeting with Frosinone on Saturday.
Napoli are currently ninth in the Serie A table, while Frosinone sit sixth.
