Michael Lohan -- Complications Push Back Heart Surgery

Michael Lohan did not have surgery as planned yesterday, TMZ has learned, because doctors discovered additional blood clots in his lung which required treatment before they could operate.

As TMZ first reported, Lohan was rushed to the hospital on Thursday after complaining of chest pains and doctors determined he needed surgery.

According to our sources, doctors discovered blood clots in one of his lungs in their original examination ... but discovered more yesterday. So, we're told, they put him on medication to break down the clots and rescheduled the surgery for Monday.