Video: Surface anatomy of the heart

Since the dawn of time, mankind has yearned to know the deepest mysteries of the heart to decipher the intricacies of their cherished confidant soul. Here at Kenhub, however, we've always believed that to truly fathom the secrets of the heart, you should really first acquaint yourself with its surface anatomy. Let's embrace the delicate intricacies of its form, for within its contours, lies its most hidden secrets.

Well, today's tutorial on the surface anatomy of the heart is the start. The heart is a muscular organ that pumps blood around the body by circulating it through the vascular system. It sits in the middle mediastinum between the left and right lungs, anterior to the esophagus and posterior to the sternum, in a sac-like structure called the pericardium.

The heart is sometimes described as a pyramid shape that has been tipped over onto one of its sides. If we visualize this within the thoracic cavity from an anterior view, the apex would project forward, slightly downwards, and to the left, and we would have all these other important sides of the pyramid. which we call the surfaces of the heart.

The apex of the heart is formed by the inferolateral part of the left ventricle and is positioned deep to the left fifth intercostal space, 8 to 9 centimeters from the midclavicular line.

Now let's take a look at the surfaces of the heart in a bit more detail.

First, we have the posterior surface, also known as the base of the heart. This is also the base that the pyramid rests on. It has a roughly quadrilateral shape that lies anterior to the main bronchi and esophagus. It consists of the left atrium, a small portion of the right atrium, and the proximal parts of the great veins, including the coronary sinus, left and right pulmonary veins, and the superior and inferior vena cavae. The left atrium receives oxygenated blood from the lungs via four pulmonary veins and pumps it into the left ventricle.

Next, we have the anterior surface of the heart, also known as the sternocostal surface, which consists of the right atrium, two-thirds of the right ventricle, and a third of the left ventricle. It lies adjacent to the body of the sternum and the third to sixth costal cartilages.

The left ventricle is the largest of all heart chambers, mainly due to the thickness of its muscular walls. It occupies most of the left pulmonary and inferior surfaces of the heart. The right ventricle has a triangular shape and a large part of the anterior surface of the heart is formed by its anterosuperior border. Its inferior surface rests on the diaphragm. The right ventricle functions to pump deoxygenated blood to the lungs.

The anterior surface also has some key landmarks. This includes the auricles which are pectinated muscle structures that form a distinctive pouch on the exterior surface of the heart. The left auricle overlaps the root of the pulmonary trunk while the right auricle overlaps the ascending aorta.

Some other key landmarks include the coronary sulcus. The coronary sulcus is also known as the atrioventricular groove and it separates the atria and ventricles of the heart. We also have the anterior interventricular sulcus and this is a line of demarcation between the left and right ventricles. It extends from the coronary sulcus to the apex of the heart.

Then we have the inferior surface of the heart, which consists of the left ventricle and a small portion of the right ventricle. It mainly sits on the central tendon of the diaphragm. On this surface, we have several key landmarks that we can visualize. First, we have the inferior interventricular sulcus. This sulcus defines the boundary between the left ventricle and the right ventricle.

Since the heart sits between the lungs, it makes sense that its lateral sides are called the left and right pulmonary surfaces of the heart.

The left surface of the heart consists of the lateral portion of the left ventricle as well as a small part of the left atrium and the left auricle of the heart. On this surface, we can also spot the coronary sulcus. Then we have the right surface of the heart which is found between the terminations of the superior and inferior vena cavae. The right surface of the heart is mostly composed of the right atrium. The right atrium is the first chamber of the heart to receive deoxygenated blood from the body via superior and inferior vena cavae as well as the coronary sinus.

Speaking of the venae cavae, the heart has some other important major vessels that we can see on its surface. These vessels circulate oxygenated and deoxygenated blood from the heart to the body or from the lungs to the heart.

The superior vena cava is one of the great vessels of the heart. It carries deoxygenated blood from the upper portion of the body and drains into the right atrium. The superior vena cava is formed by the right and left brachiocephalic veins and begins approximately at the level of the junction of the second and third thoracic vertebrae.

The inferior vena cava is a large vein that ascends from the abdominal cavity through the diaphragm, entering the thoracic cavity and draining into the right atrium. It carries deoxygenated blood from the lower portion of the body to the heart.

The aorta is the largest blood vessel in the body and it initially ascends through the thoracic cavity before it arches and descends behind the heart into the abdomen. The ascending aorta is the first segment of the aorta and starts at the aortic valve and ends at the level of the second right sternocostal joint and is approximately 5 centimeters in length. Two arteries originate from the ascending aorta – the left and the right coronary arteries.

The aortic arch is a continuation of the ascending aorta. It begins posterior to the second right sternocostal joint at the level of the sternal angle. It then arches superoposteriorly and to the left. The aortic arch passes anterior to the right pulmonary artery and the bifurcation of the trachea. The aortic arch gives rise to three branches that supply the head, neck, and upper limbs.

The brachiocephalic trunk is the first branch of the aortic arch. The brachiocephalic trunk and its branches supply blood to the right arm, head, and neck. The left common carotid artery is the second branch of the aortic arch. This artery supplies blood to the head and neck. The left subclavian artery is the third branch of the aortic arch whose function is to supply blood to the left upper limb and also the head via its branch, the vertebral artery.

Another major vessel is the pulmonary trunk. The pulmonary trunk emerges from the right ventricle and carries deoxygenated blood from the heart to the lungs. The trunk is a short and wide structure that is about 5 centimeters in length and 3 centimeters in diameter. It branches into two pulmonary arteries – the left pulmonary artery and the right pulmonary artery.

Similarly, we have the pulmonary veins that are large blood vessels that receive oxygenated blood from the lungs to deliver to the rest of the body. There are four pulmonary veins in total – two left pulmonary veins and two right pulmonary veins. These veins come from each lung and drain into the left atrium of the heart.

So, we've seen all the different surfaces of the heart and the important vessels found on these surfaces, but what separates these surfaces from each other are the heart's borders.

Firstly, we have the right border of the heart. This line runs mainly over the right atrium, extending between the superior and inferior venae cavae, and over a small portion of the right ventricle. This corresponds to a line drawn from the third right costal cartilage to the sixth right costal cartilage.

Then there is the left border of the heart that separates the left and anterior surfaces. It is mainly formed by the left ventricle and part of the left auricle. It corresponds to a line drawn from the inferior border of the second left costal cartilage to the intersection points between the fifth left intercostal space and midclavicular line. More simply, the line interconnects the left ends of the superior and inferior borders of the heart.

The superior border of the heart is a line that goes over the roots of the aorta and pulmonary trunk and a small portion of the left and right auricle. This corresponds to a line connecting the inferior border of the second left costal cartilage to the superior border of the third right costal cartilage.

Lastly, the inferior border of the heart extends along the right ventricle and part of the left ventricle at its apex. This corresponds to a line drawn from the inferior end of the right border at the sixth costal cartilage to the point where the fifth left intercostal space and midclavicular line intersect. This point of the intersection marks the apex of the heart.

Now that we've acquainted ourselves with what lies on the surface of our hearts, perhaps it's time to start peeling back the layers and delving into the captivating mysteries within by checking out our other study units and content on the heart. After all, there's a whole world of wonder waiting to be discovered beneath the surface.