![apex of heart apex of heart](https://ars.els-cdn.com/content/image/3-s2.0-B9780128008836000471-f47-02-9780128008836.jpg)
Through much of development there is a physiological communication between the ventricles at the tip of the septum allowing free mixing of right and left ventricular blood as it travels through a common outflow tract. The right and left ventricles are already separated to a great extent by the muscular interventricular septum arising from the apex of the heart. We introduce the function of the heart here by tracing the flow of blood through it. The right and left atria are two thin-walled sacs that collect blood either from the veins (right atria) or from the lungs (left atria), whereas the ventricles are thick-walled muscular sacs that propel blood though the arteries. The heart itself is built around a ring of fibrous tissue called the annulus fibrosus that separates the atria from the ventricles and contains the four heart valves, as shown in Figure 5.4.6. This can be felt in the fifth left intercostal space. With every beat, the heart twists forward and the apex taps against the chest wall, producing the apex beat. The heart sits atop the diaphragm and its apex is close to the anterior surface of the thoracic cavity. The pericardium is fused to the diaphragm, and so downward movement of the diaphragm during inspiration pulls the heart into a more vertical orientation.
![apex of heart apex of heart](https://d16qt3wv6xm098.cloudfront.net/Gz1OObjLTq6xsQvp8l_hdI0gQBO7G4FY/_.jpg)
It is suspended within a tough fibrous sac, the pericardium, by its connections to the great vessels: the superior and inferior venae cavae, the pulmonary artery and veins, and the aorta.
![apex of heart apex of heart](http://bodterms.weebly.com/uploads/5/4/1/9/5419033/325447.jpg)
The heart is located in the middle of the thoracic cavity, oriented obliquely, with the apex of the heart pointing down and to the left, as shown in Figures 5.4.1 and 5.4.2.