 So when we think about coronary artery disease, there are basically three different types of angina, which is first of all, stable angina, which is basically the patient's complaining of chest pain with activity. So when there's increased oxygen demand because the patient is walking, they might get excited, they might get an argument. There's increased oxygen demand and so then their cardiac muscle is not able to perfuse that partially clogged artery and they're having chest pain. But when they rest or take medications, specifically nitroglycerin, the pain goes away. So stable angina, pain with a predicted amount of activity relieved by a predicted amount or predicted activity or intervention such as the medication nitroglycerin or risk. Now, the more severe case is the unstable angina, which basically means that the patient has chest pain and rest. So now they're just resting, they're not exerting themselves, they're not physically active, but they are having chest pain, which means when we look back at our artery that that artery is getting more and more clogged. So now there's no perfusion going through or maybe just a tiny bit and there is nothing that the patient needs more oxygen for because they're completely at rest and now they're having chest pain. Now that is a warning sign that something is going on and we need to intervene very quickly. And it says here it's a precursor to MI, so myocardial infarction. And here we need to determine between the two types of myocardial infarction, which is the STEMI, so ST elevation myocardial infarction or non-STEMI, so it doesn't have that ST elevation. And down here I've drawn out a picture of your normal cardiac cycle. And some of you might not have learned exactly what a dysrhythmia means or what an ST elevation means, so for the purposes of this video we'll just very briefly cover that. So as you probably remember from your physiology class, the normal cardiac cycle has a P, Q, R, S and a T wave and this is just the normal EKG line that you would look at. And so we have the baseline which is where the P starts and the T ends and they are both at the same level. Now when there's an ST elevation MI that means that the ST element is elevated and again I've drawn that out here. So it again starts at this baseline and ends at the baseline. We have the P, Q, R, ST, but as you see this ST here is elevated. And that usually means if you see that on an EKG that's a warning sign that currently right now this patient's heart is not being profused. It can either be because of ischemia, so less oxygen flow or complete infarction. And at this point when we're running the EKG we don't really exactly know and then we'll get into more diagnostic tests to determine what's going on with this patient. But ST elevation means that this segment of the EKG is elevated. Sometimes they also call it a fireman's hat, but because if you look at it it could look like a fireman's hat. So that's another way to remember. Now the third possible angina or acute coronary syndrome is called Prince Meadows angina, also known as variant angina. And that basically is a little bit of a different kind of angina and that means that the spasm or that the patient's pain is caused by coronary artery spasm, which is a completely different cause than this plaque buildup that we have there. Although it can still lead to complications, but typically the patient is treated with calcium channel blockers and that keeps the symptoms at bay. Of course they're going to need special investigation to make sure that nothing else is going on, but this is a different kind of angina from the stable and unstable.