The singer tweeted from her bed in Watford General Hospital, along with a photo of herself attached to medical equipment.
"Not exactly how I'd imagined my Sunday ... Overnight stay Needed," she wrote with her photo.
She soon uploaded a second photo of her baby Faith and partner Hugh Hanley, saying: "But baby faith and my @hughhanley keeps a smile on my face."
Heaton later reassured her followers that she was fine, adding: "As you may or may not know I have suffered from long and scary heart problems over the years. Today it took a turn for the worst.
"I am ok now, I am being kept in over night just 4 monitoring.. #nhs are amazing and have looked after me so well. Thank u #watfordgeneral."
Posting another photo of Faith, she concluded: "I am ok now, I am being kept in over night just 4 monitoring.. #nhs are amazing and have looked after me so well. Thank u."
Michelle Heaton recently stated that her former group Liberty X would only reunite for a one-off gig if they did reform.