The 55-year-old tweeted from the hospital in Tooting to thank the professionals who "saved his life".
Moore won 64 England caps between 1987 and 1995, played for the British and Irish Lions, and trained as a solicitor while pursuing his rugby career.
The former England hooker now works in the media.
Former England rugby international Brian Moore is recovering in intensive care at St George's hospital in London after suffering a heart attack.