The Heart Anatomy

II. EXTERNAL CONFIGURATION

The heart is formed by four chambers: the right and left atria and the right and left ventricles.

Cardiac Sulci (Sutures)

The boundaries of the atria and ventricles are marked externally by the interventricular, interatrial, and atrioventricular sulci.

• The atrioventricular sulcus is situated in a plane perpendicular to the long axis of the heart.

• The interventricular and interatrial sulci are arranged along a vertical plane passing through the long axis.

• These sulci contain the coronary vessels and are filled by these vessels and the surrounding fat.

Faces

The heart presents three faces:

• The Anterior Face (Sterno-costal) faces forward, to the right, and slightly upward.

• The Inferior Face (Diaphragmatic) is slightly convex.

• The Lateral Left Face is convex and faces upward and backward. Each face is divided by the atrioventricular sulcus into a ventricular segment and an atrial segment.

Borders

• The right border is sharp (acute).

• The left borders are rounded; they separate the lateral left face from the anterior and inferior faces.

Base and Apex

• The Base is mainly constituted by the atria. It is divided by the interatrial sulcus into a right segment (convex) and a left segment (concave, where the coronary sinus continues).

• The Apex (apex cordis) is divided by a slight depression connecting the anterior and posterior interventricular sulci. The larger left part belongs to the left ventricle and forms the apex itself.

III. HEART RELATIONS AND CARDIAC AREA

The heart is surrounded by the pericardium, a fibro-serous envelope.

Organic Relations

• The anterior face is related to the thymus or its remnants, the lungs, and the pleurae, as well as the sterno-costal framework.

• The inferior face rests upon the diaphragm, specifically the anterior leaflet of the central tendon.

• The left face corresponds to the pleura and the cardiac impression of the left lung; it is crossed by the phrenic nerve and the superior left phrenic arteries.

• The left segment of the base (left atrium) is related posteriorly to the organs of the posterior mediastinum, especially the esophagus, via the oblique sinus of the pericardium. This segment projects posteriorly across the height of the sixth, seventh, and eighth thoracic vertebrae.

Thoracic Projection (Cardiac Area)

For a thorax of average dimensions, the cardiac area is a quadrilateral:

• The two superior angles are located in the middle part of the second intercostal space, approximately 1 cm from the lateral sternal border.

• The inferior right angle is at the sternal extremity of the sixth right intercostal space.

• The inferior left angle is located in the fifth left intercostal space, approximately 8 cm lateral to the midline.

IV. INTERNAL CONFIGURATION

Septa (Partitions)

Interventricular Septum The septum has a large muscular part and a smaller membranous part. The thickness of the membranous part does not exceed 2 mm, and its height and length measure about 7 to 8 mm.

Interatrial Septum This is a thin membrane separating the two atria.

• Its right face presents the fossa ovalis, a depression limited by the limbus of the fossa ovalis.

• Its left face presents the valve of the foramen ovale, a vestige of the fetal foramen ovale.

• An adult may display remnants of a small fossa, sometimes called the preseptal fossa (Rouvière), anterior to this semilunar fold.

Atria

Right Atrium

• The superior wall contains the ostium of the superior vena cava, which measures approximately 20 mm in diameter.

• The inferior wall contains the ostia of the inferior vena cava and the coronary sinus.

• The ostium of the inferior vena cava is circular, measuring 30 mm in diameter. Its anterior border bears the valve of the inferior vena cava.

• The ostium of the coronary sinus is provided with the valve of the coronary sinus.

Left Atrium

• The posterior wall presents the four ostia of the pulmonary veins.

• The anterior wall contains the left atrioventricular ostium and the opening of the auricle.

Ventricles

Right Ventricle Its walls measure approximately 0.5 cm in thickness.

• Right Atrioventricular Ostium (Tricuspid Valve) The circumference measures about 120 mm in men and 105 mm in women (Testut). The valve is divided into three principal triangular cusps.

• Pulmonary Trunk Ostium (Infundibulum / Arterial Cone) The orifice is situated high up and is provided with three semilunar valves.

• The Trabecula Septo-Marginalis is a secondary order fleshy column connected with the atrioventricular bundle.

Left Ventricle Its average thickness is greater than 1 cm.

• Left Atrioventricular Ostium (Mitral Valve) The circumference measures about 110 mm in men and 90 mm in women. The valve is composed of two quadrangular cusps, with the right cusp being larger than the left.

• Papillary Muscles (Pillars) It has two principal pillars: the anterior pillar and the posterior pillar.

• Aortic Ostium Located anteriorly and to the right of the left atrioventricular ostium. It is circular, with a circumference of approximately 65 to 70 mm. It is equipped with three semilunar valves. The fibrous nodule on the free border is called the nodule of the semilunar valves.

V. STRUCTURE OF THE HEART

Myocardium and Fibrous Skeleton

The heart is an essentially muscular organ.

• The Fibrous Skeleton is composed of four fibrous rings (two atrioventricular and two arterial). The aortic ring presents an expansion of the fibrous skeleton posteriorly.

Conduction System (Cardio-Nector)

• The Sinu-Atrial Node begins subpericardially, on the external side of the superior vena cava ostium.

• The Atrioventricular Bundle (Bundle of His) originates in the atrial wall, near the ostium of the coronary sinus. It divides into right and left bundles.

Endocardium

The endocardium is the internal tunic: a thin, smooth, adherent membrane that covers the entire internal surface of the atria and ventricles and is continuous with the internal tunic of the vessels.

VI. VASCULATURE AND INNERVATION

Coronary Arteries

The two coronary arteries, right and left, are anastomosed with each other in 97% of cases.

• Left Coronary Artery It originates from the aorta, at or immediately above the left semilunar valve. It runs through the anterior interventricular sulcus and often terminates near the posterior interventricular sulcus, at a distance from the apex varying between 1 and 3 cm. The atrioventricular branch gives off branches to the left atrium and ventricle.

• Right Coronary Artery This artery is more voluminous than the left. It originates at or immediately above the right semilunar valve. It follows the atrioventricular sulcus, enters the posterior interventricular sulcus, and frequently anastomoses with the left coronary artery.

Veins of the Heart

• Great Cardiac Vein and Coronary Sinus The great cardiac vein forms the coronary sinus, a dilated terminal conduit measuring about 3 cm in length on average. The coronary sinus collects the venous blood from almost the entire heart.

• Smallest Cardiac Veins (Veins of Thebesius) These open into the adjacent chambers (atria or ventricles) through small openings (foramina).

Nerves

The cardiac plexus is formed by branches of the vagus nerves (parasympathetic) and the sympathetic nervous system. The visceral layer of the serous pericardium is innervated by the subpericardial nervous plexus.

VII. PERICARDIUM

Pericardial Layers and Sinuses

The pericardium is a fibro-serous sac enveloping the heart. The serous pericardium comprises a visceral layer and a parietal layer, limiting the virtual pericardial cavity.

• Vascular Reflections The visceral layer reflects to form two vascular sheaths around the arterial pedicle (aorta and pulmonary trunk) and the venous pedicle (cavae and pulmonary veins).

• The Transverse Sinus of the Pericardium is limited anteriorly by the arterial pedicle.

• The Oblique Sinus of the Pericardium is a large cul-de-sac extending over the posterior surface of the left atrium. This recess may open into the superior border of the inferior omental recess in about 60% of cases, thus being a dependency of the peritoneal cavity (Broman, Favaro, etc.).

Fibrous Pericardium and Ligaments

The fibrous pericardium is a thick fibrous membrane external to the parietal serous layer.

• Ligaments The pericardium is attached to adjacent structures by ligaments:

    ◦ Phreno-pericardial ligaments are dependencies of the endothoracic fascia.

    ◦ Sterno-pericardial ligaments (superior and inferior).

    ◦ Vertebro-pericardial ligaments. These bands extend up to the sixth cervical vertebra and the fourth thoracic vertebra.

• Fatty Fringes Fatty fringes are fixed to the fibrous pericardium, designed to fill the free spaces between the pericardium, lungs, and diaphragm.

Pericardial Vascularization

• The visceral layer of the serous pericardium is supplied by the coronary arteries.

• The nerves of the parietal layer are derived from the phrenic, vagus, and sympathetic nerves.