The invention provides methods for early diagnosis or detection of acute coronary syndrome and prediction of adverse cardiac events on the basis of elevations of catalytic iron in biological fluid of a human subject. An embodiment of the invention provides a method for early detection of acute coronary syndrome (ACS) in a human subject at the time of presentation of the chest pain. The method includes analyzing a test sample of the biological fluid for amount of catalytic iron and detecting acute coronary syndrome in the human subject.