The team announced the operation on Monday but gave no further details. It said he is expected to make a full recovery and gave no timetable for his return.
Armstead is on the non-football injury list and has not participated in training camp since it began on Thursday.
A heart condition sidelined Armstead for his senior season at Southern California in 2011. He wasn't drafted by an NFL team and played last season in the Canadian Football League. Patriots coach Bill Belichick has said Armstead's current condition is unrelated to any health issues he had in college.
Copyright 2013 by The Associated Press