If you have angina and it is not relieved by Nitroglycerin, it is called Unstable Angina. Myocardial infarction describes necrosis or death of myocardial cells. Atherosclerotic heart disease is the most common underlying cause of myocardial infarction. The appearance of pathological Q waves is the most characteristic ECG finding of transmural myocardial infarction of the left ventricle. A pathological Q wave is defined as an initial downward deflection of a duration of 40 msec or more in any lead except III and aVR. The Q wave appears when the infarcted muscle is electrically inert and the loss of forces normally generated by the infarcted area leaves unbalanced forces of variable magnitude in the opposite direction from the remote region, for example, an opposite wall. These forces can be represented by a vector directed away from the site of infarction and seen as a negative wave (Q wave) by electrodes overlying the infarcted region. However, it would be wise for you to go to call 911 immediately so you can be attended in the ER and appropriate tests (EKG, serum cardiac markers, heart catheterization etc ) can be done to determine if you have either an Unstable Angina or heart attack (Myocardial Infarction). American Heart Association states that you should be seen immediately (within 4 hrs after onset of chest pain) to save the cardiac muscle. Remember Time is muscle!