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For all its potency, the cone-shaped heart is relatively small, about the size of the closed fist, about 12 cm long, 9 cm wide at its widest, and 6 cm thick. Its mass is on average 250 g in adult women and 300 g in adult men.
The cChest Heart Positionprayer rests on the diaphragm near the midline of the thoracic cavity in the mediastinum, the mass of tissue extending from the sternum to the spine; and between the lining (pleuras) of the lungs. About 2/3 of heart mass is to the left of the midline of the body. The position of the heart in the mediastinum is most easily appreciated by examining its extremities, surfaces, and boundaries. The pointed end of the heart is the apex, directed forward, down and to the left. The widest portion of the heart, opposite the apex, is the base, directed backwards, upwards and to the right.
Relationship of the Heart to the Costal Spaces

Anatomical Position of the HeartHeart Limits: The anterior surface is just below the sternum and ribs. The inferior surface is the part of the heart that mostly rests on the diaphragm, corresponding to the region between the apex and the right approach. The right border is toward the right lung and extends from the bottom surface to the base; The left border, also called the pulmonary border, faces the left lung, extending from the base to the apex. The upper limit is the great vessels of the heart and later the trachea, esophagus and descending aorta.

HEART LIMITS - Upper, Lateral, and LowerHEART LIMITS - Anterior and Posterior


Source: NETTER, Frank H .. Atlas of Human Anatomy. 2 ed. Porto Alegre: Artmed, 2000.

Cardiac Wall Layers:

Pericardium: the membrane that covers and protects the heart. It restricts the heart to its position in the mediastinum, yet allows sufficient freedom of movement for vigorous and rapid contractions. The pericardium consists of two main parts: fibrous pericardium and serous pericardium.

Heart with pericardial sacHeart with pericardial sac

The superficial fibrous pericardium
It is an irregular, dense, resistant and inelastic connective tissue. It resembles a sac, which rests on and attaches to the diaphragm.

The serous pericardiumDeeper is a thinner and more delicate membrane that forms a double layer, surrounding the heart. The outermost parietal layer of the serous pericardium is fused to the fibrous pericardium. The innermost visceral layer of the serous pericardium, also called the epicardium, adheres strongly to the surface of the heart.

Heart with pericardial sac
Epicardium: The outer layer of the heart is a thin layer of serous tissue. The epicardium is continuous from the base of the heart with the inner lining of the pericardium, called the visceral layer of the serous pericardium.


Source: NETTER, Frank H .. Atlas of Human Anatomy. 2 ed. Porto Alegre: Artmed, 2000.

Myocardium: is the middle and thickest layer of the heart. It is composed of striated cardiac muscle. It is this type of muscle that allows the heart to contract and therefore to thrust blood, or force it into the blood vessels.

Endocardium: is the innermost layer of the heart. It is a thin layer of tissue made up of simple squamous epithelium over a layer of connective tissue. The smooth and shiny surface allows blood to flow easily over it. The endocardium also coats the valves and is continuous with the lining of blood vessels entering and leaving the heart.

Heart Layers


The heart has three faces and four margins:


  • Anterior Face (Sternocostal) & #8211; Formed mainly by the right ventricle.
  • Diaphragmatic Face (Lower) & #8211; Formed mainly by the left ventricle and partially by the right ventricle; It is mainly related to the central tendon of the diaphragm.
  • Lung Face (Left) & #8211; Formed mainly by the left ventricle; It occupies the cardiac impression of the left lung.

Faces of the Heart


  • Right bank & #8211; Formed by the right atrium and extending between the superior and inferior vena cavae.
  • Lower Margin & #8211; Formed mainly by the right ventricle and slightly by the left ventricle.
  • Left margin & #8211; Formed mainly by the left ventricle and slightly by the left atrium.
  • Top margin & #8211; Formed by the right and left atria and atria in an anterior view; the ascending part of the aorta and the pulmonary trunk emerge from the superior margin, and the superior vena cava enters its right side. Posterior to the aorta and pulmonary trunk and anterior to the superior vena cava, the upper margin forms the lower limit of the transverse sinus of the pericardium.

Heart Margins


Externally the atrioventricular ostia correspond to the coronary sulcus, which is occupied by coronary arteries and veins, this sulcus surrounds the heart and is interrupted anteriorly by the aorta and pulmonary trunk.
The interventricular septum on the anterior surface corresponds to the anterior interventricular sulcus and on the diaphragmatic face to the posterior interventricular sulcus.

The interventricular sulcus ends less than a few centimeters from the right of the apex of the heart, corresponding to the notch of the apex of the heart.

The anterior interventricular sulcus is occupied by the anterior interventricular vessels.

This groove is occupied by the posterior interventricular vessels.

The posterior interventricular sulcus starts from the coronary sulcus and descends toward the notch of the apex of the heart.

External Heart Configuration

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HeartThe heart has four chambers: two atria and two ventricles. The Atriums (the upper chambers) receive blood; the Ventricles (lower chambers) pump blood out of the heart

On the front of each atrium is a wrinkled, sac-shaped structure called the auricle (similar to a dog's ear).

The right atrium is separated from the left by a thin partition called the interatrial septum; the right ventricle is separated from the left by the interventricular septum.

Heart Cavities
Source: NETTER, Frank H .. Atlas of Human Anatomy. 2 ed. Porto Alegre: Artmed, 2000.

Right atrium

The right atrium forms the right edge of the heart and receives blood rich in carbon dioxide (venous) from three veins: superior vena cava, inferior vena cava and coronary sinus.

The superior vena cava collects blood from the head and upper body, the lower one receives blood from the lower parts of the body (abdomen and lower limbs) and the coronary sinus receives the blood that nourished the myocardium and takes the blood to the right atrium. .

While the posterior wall of the right atrium is smooth, the anterior wall is rough due to the presence of muscle ridges, called pectinate muscles.

Blood passes from the right atrium to the right ventricle through a valve called the tricuspid (formed by three leaflets & #8211; valves or cusps).

In the medial wall of the right atrium, which consists of the interatrial septum, we find a depression that is the fossa ovalis.

Formerly, the right atrium has a pyramidal expansion called the right atrium, which serves to dampen the impulse of blood as it enters the atrium.

The holes where the vena cavae open have the names of ostia of the vena cavae.

The opening of the coronary sinus is called the coronary sinus ostium and we also find a slide that prevents blood from returning from the atrium to the coronary sinus which is called the coronary sinus valve.

Left atrium

The left atrium is a thin-walled cavity with smooth posterior and anterior walls that receives the already oxygenated blood; through four pulmonary veins. Blood passes from the left atrium to the left ventricle through the Bicuspid valve (mitral), which has only two cusps.

The left atrium also has a pyramidal expansion called the left atrium.


The right ventricle forms most of the anterior surface of the heart. Its interior has a series of high bundles of cardiac muscle fibers called fleshy trabeculae.

In the right atrioventricular ostium there is a device called Tricuspid valve which prevents blood from returning from the ventricle to the right atrium. This valve consists of three whitish and irregularly triangular membrane blades, with the base implanted at the edges of the ostium and the apex directed downward and attached to the ventricle walls by filaments.

Each blade is called a cusp. We have an anterior, another posterior, and another septal cusp.

The apex of the cusps is trapped by filaments called Tendon Ropes, which fall into small fleshy columns called Papillary muscles.

The pulmonary trunk valve is also made up of small blades, but these are arranged in a shell, called semilunar valves (anterior, left and right).



Atrioventricular Valve Structure
In the center of the free border of each of the valves we find small nodules called semilunar (pulmonary) valve nodules.



The left ventricle forms the apex of the heart. In the left atrioventricular ostium, we find the left atrioventricular valve, consisting only of two laminae called cusps (anterior and posterior). These valves are called bicuspids. Like the right ventricle, it also has fleshy trabeculae and tendon cords that attach the bicuspid valve cusps to the papillary muscles.

Blood passes from the left atrium to the left ventricle through the left atrioventricular ostium where the Bicuspid valve (mitral). From the left ventricle, blood exits to the largest artery in the body, the ascending aorta, through the Aortic valve & #8211; consisting of three semilunar valves: right, left and posterior. Hence, part of the blood flows to the coronary arteries, which branch from the ascending aorta, bringing blood to the heart wall; the remaining blood passes to the aortic arch and descending aorta (thoracic aorta and abdominal aorta). Branches of the aortic arch and descending aorta carry blood throughout the body.

The left ventricle receives oxygenated blood from the left atrium. The main function of the left ventricle is to pump blood to the systemic circulation (body). The left ventricular wall is thicker than that of the right ventricle. This difference is due to the greater force required to pump blood into the systemic circulation.

Source: NETTER, Frank H .. Atlas of Human Anatomy. 2 ed. Porto Alegre: Artmed, 2000.

Cardiac cycle

A single heart cycle includes all events associated with a heartbeat. In the normal cardiac cycle the two atria contract, while the two ventricles relax and vice versa. The term systole designates the contraction phase; The relaxation phase is called diastole.

Bicuspid Valve Cusps
When the heart beats, the atria contract first (atrial systole), forcing blood to the ventricles. Once filled, the two ventricles contract (ventricular systole) and force the blood out of the heart.


 Valves in Ventricular Diastole          Valve Dynamism     Valves in Ventricular Systole

For the heart to be efficient in its pumping action, it takes more than the rhythmic contraction of its muscle fibers. The direction of blood flow should be oriented and controlled, which is obtained by four valves previously mentioned: two located between the atrium and the ventricle & #8211; atrioventricular (tricuspid and bicuspid valve); and two located between the ventricles and the large arteries that carry blood out of the heart & #8211; semilunar (pulmonary and aortic valve) .Complement: The valves and valves are to prevent this abnormal blood behavior, to prevent reflux from occurring, they close after the blood has passed.

Systole It is the contraction of the heart muscle, we have atrial systole that pushes blood to the ventricles. Thus the atrioventricular valves are open to blood flow and the pulmonary and aortic valves are closed. In ventricular systole, the atrioventricular valves are closed and the semilunar valves open to the passage of blood.

VENTRICULAR SYMPTOM & #8211; ACTION OF Atrio-Ventricular Valves
 Ventricular Syndrome - Action of the Atrio-Ventricular Valves
Source: NETTER, Frank H .. Atlas of Human Anatomy. 2 ed. Porto Alegre: Artmed, 2000.
VENTRICULAR DIASTOLE & #8211; ACTION OF Atrio-Ventricular Valves
Source: NETTER, Frank H .. Atlas of Human Anatomy. 2 ed. Porto Alegre: Artmed, 2000.

In conclusion we can say that the cardiac cycle comprises:
1- Atrial systole
2- Ventricular systole
3- Ventricular Diastole


The heart is irrigated by the coronary arteries and the coronary sinus.
The coronary arteries are two, one right and one left. They have this name because both run through the coronary sulcus and are both originating from the aortas artery.

Immediately after its origin, the artery goes to the coronary sulcus running from right to left until it anastomoses with the circumflex branch, which is the terminal branch of the left coronary artery that continues the sulcus. coronary.

The Right Coronary Artery: from the origin to two arteries that will irrigate the right margin and the posterior part of the heart, they are right marginal artery and posterior interventricular artery.

The Left Coronary ArteryInitially, it passes through a branch behind the pulmonary trunk to reach the coronary sulcus, showing itself near the apex of the left atrium.

Immediately after, it emits an anterior interventricular branch and a circumflex branch that originates the left marginal artery.

On the diaphragmatic face the two arteries anastomose to form a circumflex branch.

Venous blood is collected from several veins that flow into the great heart vein, which starts at the apex of the heart, rises the anterior interventricular sulcus and follows the left-to-right coronary sulcus through the diaphragmatic face to flow into the atrium. right.

The terminal portion of this vessel, represented by its last 3 cm, forms a dilation that is named coronary sinus.

The coronary sinus also receives the middle heart vein, which runs from the bottom up the posterior interventricular sulcus and the small heart vein that borders the right edge of the heart.

There are still very small minimal veins that flow directly into the cardiac cavities.


The innervation of the heart muscle is in two ways: extrinsic from nerves outside the heart and intrinsic from a system found only in the heart and located within.

Extrinsic innervation derives from the autonomic nervous system, that is, sympathetic and parasympathetic.

From the sympathetic, the heart receives the sympathetic cardiac nerves, being three cervical and four or five thoracic.
The parasympathetic fibers going to the heart follow the vagus nerve (X cranial nerve), from which parasympathetic cardiac nerves are derived, two cervical and one thoracic.

Physiologically the sympathetic accelerates and the parasympathetic slows down the heartbeat.

The intrinsic innervation or conduction system of the heart is the reason for the continuous heartbeat. It is an intrinsic, rhythmic electrical activity that originates in a network of specialized cardiac muscle fibers called auto-rhythmic cells (cardiac pacemakers) because they are self-exciting.

Cardiac excitation begins at the sinoatrial node (SA), located in the right atrial wall, inferior to the opening of the superior vena cava. Propagating along the atrial muscle fibers, the action potential reaches the atrioventricular (AV) node, located in the interatrial septum, anterior to the opening of the coronary sinus. From the AV node, the action potential reaches the atrioventricular bundle (His bundle), which is the only electrical connection between the atria and the ventricles. After being conducted along the AV bundle, the action potential enters the right and left branches, which cross the interventricular septum, towards the cardiac apex. Finally, conductive myofibers (Purkinge fibers) rapidly conduct the action potential, first to the apex of the ventricle and then to the rest of the ventricular myocardium.



Source: NETTER, Frank H .. Atlas of Human Anatomy. 2 ed. Porto Alegre: Artmed, 2000.

Diastole is the relaxation of the heart muscle, when the ventricles are filled with blood, at this time the atrioventricular valves are open and the semilunar valves are closed.

Structures of
Cardiovascular system

Blood vessels

Arterial system

Venous system