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The heart has different layers: endocardium (innermost, touches blood), myocardium (muscle, contracts), and epicardium (outermost, fibrous tissue). Fibrous pericardium connects heart to diaphragm and sternum, while serous pericardium has visceral and parietal layers with a fluid-filled space to protect the heart during contractions. These layers prevent damage and help the heart function properly. The first layer I'll talk about is the endocardium, endo meaning innermost, and this is the layer of the heart that touches the blood, so this is the innermost layer of the chambers of the heart, the atria and the ventricles. The next layer is the myocardium, myo means muscle, so this is the muscle part of the heart, or this is the part of the heart that does the job of contracting. The cells within the myocardium are called myocytes, and these cells have the job of yes, contracting, but also many of them produce the conduction of the heart, so they have the ability to generate electrical conduction within the heart. Now, all of the myocytes have this ability, but only some of them do it, and when we get into talking about dysrhythmias of the heart, this will make a little bit more sense, because sometimes those cells decide that they're going to generate electricity when they really shouldn't be doing that. The next layer is the epicardium, the epicardium meaning the outermost layer, epi meaning outermost. This is the outermost layer of the heart, now it is protected by some additional layers, but the epicardium is a fibrous and loose connective tissue on the outer part of the heart. Next we have the fibrous pericardium, and so the fibrous pericardium is a couple layers beyond the epicardium, we'll talk about the next one close to the epicardium in a moment, but the fibrous pericardium is that part of the heart, that membrane that connects the heart to the diaphragm and to the sternum to hold it into place. Then we have the serous pericardium, the serous pericardium is made up of a couple layers, the visceral and parietal pericardium, so just like in the lungs where we have the visceral and the parietal pleura, the heart has a visceral and parietal pericardium, so just protective layers just like in the lungs, and in between them is a cavity or a space that holds fluid, a serous fluid that we call pericardial fluid, in the lungs we call that a pleural fluid, and this just allows for the heart to fill and contract without becoming damaged, so these two layers slide against each other just like they do when the lungs expand.