The chordae tendineae pull on the AV valves to keep them from folding backwards and allowing blood to regurgitate past them. The AV valves are attached on the ventricular side to tough strings called chordae tendineae. The AV valve on the left side of the heart is called the mitral valve or the bicuspid valve because it has two cusps. The AV valve on the right side of the heart is called the tricuspid valve because it is made of three cusps (flaps) that separate to allow blood to pass through and connect to block regurgitation of blood. The atrioventricular (AV) valves are located in the middle of the heart between the atria and ventricles and only allow blood to flow from the atria into the ventricles. The heart valves can be broken down into two types: atrioventricular and semilunar valves. To prevent blood from flowing backwards or “regurgitating” back into the heart, a system of one-way valves are present in the heart. The heart functions by pumping blood both to the lungs and to the systems of the body. The right side of the heart maintains pulmonary circulation to the nearby lungs while the left side of the heart pumps blood all the way to the extremities of the body in the systemic circulatory loop. This difference in size between the sides of the heart is related to their functions and the size of the 2 circulatory loops. The chambers on the right side of the heart are smaller and have less myocardium in their heart wall when compared to the left side of the heart. The ventricles are connected to the arteries that carry blood away from the heart. The ventricles are the larger, stronger pumping chambers that send blood out of the heart. The atria act as receiving chambers for blood, so they are connected to the veins that carry blood to the heart. The atria are smaller than the ventricles and have thinner, less muscular walls than the ventricles. The heart contains 4 chambers: the right atrium, left atrium, right ventricle, and left ventricle. The right side of the heart has less myocardium in its walls than the left side because the left side has to pump blood through the entire body while the right side only has to pump to the lungs. The ventricles, on the other hand, have a very thick myocardium to pump blood to the lungs or throughout the entire body. The atria of the heart have a very thin myocardium because they do not need to pump blood very far-only to the nearby ventricles. The thickness of the heart wall varies in different parts of the heart. The endocardium is very smooth and is responsible for keeping blood from sticking to the inside of the heart and forming potentially deadly blood clots.

Endocardium is the simple squamous endothelium layer that lines the inside of the heart. Below the myocardium is the thin endocardium layer. Myocardium makes up the majority of the thickness and mass of the heart wall and is the part of the heart responsible for pumping blood. The myocardium is the muscular middle layer of the heart wall that contains the cardiac muscle tissue. Below the epicardium is the second, thicker layer of the heart wall: the myocardium. Thus, the epicardium is a thin layer of serous membrane that helps to lubricate and protect the outside of the heart. The epicardium is the outermost layer of the heart wall and is just another name for the visceral layer of the pericardium. The heart wall is made of 3 layers: epicardium, myocardium and endocardium. The pericardium has 2 layers-a visceral layer that covers the outside of the heart and a parietal layer that forms a sac around the outside of the pericardial cavity. Besides lubrication, the pericardium serves to hold the heart in position and maintain a hollow space for the heart to expand into when it is full. Pericardium is a type of serous membrane that produces serous fluid to lubricate the heart and prevent friction between the ever beating heart and its surrounding organs. The walls and lining of the pericardial cavity are a special membrane known as the pericardium. The heart sits within a fluid-filled cavity called the pericardial cavity. Because the heart points to the left, about 2/3 of the heart’s mass is found on the left side of the body and the other 1/3 is on the right. The base of the heart is located along the body’s midline with the apex pointing toward the left side.

The inferior tip of the heart, known as the apex, rests just superior to the diaphragm. Pulmonary arteries and veins, and the vena cava.

Heartbeat line