Lindsay Lohan's estranged dad was taken to hospital on Friday (27Jan12) after suffering chest pains.
Michael Lohan is currently under observation at an unspecified medical center after doctors discovered he had blood clots and put him on medication to break them up, reports TMZ.com.
It is the second time in as many months Michael has been treated in hospital - he underwent surgery to unclog an artery in December (11).
Once Lohan is stable, it is believed he will return to a court-ordered domestic violence intervention program in Palm Beach, Florida. He is due to be released on 16 March (12).