A large mostly anterior myocardial infarction without adequate and timely reperfusion therapy can lead to extensive loss of myocardial tissue. As this weakens the anterior ventrical wall, this can result in local bulging of the anterior wall. If profound this is called a cardiac aneurysm.
Cardiac aneurysms often have typical ECG characteristics: anterior Q waves and persistent ST elevation.
Patients with cardiac aneurysms have a bad prognosis due to the severely reduced ejection fraction, they often have heart failure and risk sudden death due to ventricular fibrillation.