Losmapimod is a new anti-inflammatory medication which potentially may benefit patients with Acute Coronary Syndrome, (ACS), a condition which includes heart attack. There is a growing understanding that the inflammatory response to ACS is integral to the subsequent evolution of plaque instability. Losmapimod inhibits p38 mitogen activated protein kinase (MAPK), an enzyme which may play a central role in inflammation in the setting of heart attack. Inhibition of p38 MAPK may stabilize atherosclerotic plaques, reduce the risk of subsequent plaque rupture, indirectly improve vascular function and prevent subsequent thrombosis, and thus reduce infarct size and the risk of subsequent cardiac events. This study will test whether losmapimod can safely reduce the risk of a subsequent cardiovascular event (such as death, heart attack, or near heart attack requiring urgent treatment ) when started immediately after ACS (specifically, heart attack). Patients who present with heart attack and qualify for the study will be randomly assigned to receive 3 months treatment with either losmapimod twice daily or placebo, which will be administered in addition to the usual standard of care therapies for heart attack. Following the in-hospital period, subjects will return for outpatient visits at 4 and 12 weeks, as well as a follow up visit at 24 weeks.