Summary
Highlights
The heart is a hollow, muscular organ located in the middle mediastinum, enclosed by the pericardium within the thoracic cavity. It is known as 'cardia' in Greek and 'cordis' in Latin. The heart is conical or pyramidal in shape, averaging 12 by 9 centimeters, slightly larger than a clenched fist. It weighs approximately 300g in males and 250g in females. One-third of the heart lies to the right of the median plane, and two-thirds lie to the left.
The heart has four chambers: a right atrium, left atrium, right ventricle, and left ventricle. The ventricles are directed downward and forward, while the atria are backward, upward, and to the right. The video then introduces the external features: an apex, a base, four borders (right, left, inferior, superior), and three surfaces (sternocostal, left, diaphragmatic).
The apex is directed downward, forward, and to the left, formed by the left ventricle. It lies in the left fifth intercostal space, nine centimeters from the midline. The base is opposite to the apex, directed upward, backward, and to the right. It is quadrilateral, with its left two-thirds formed by the left atrium and its right one-third by the right atrium.
The heart has four borders: the right border, formed by the right atrium, is rounded and convex. The left border, formed by the left oracle and apex, is convex upwards and leftward and is accompanied by the marginal branch of the left coronary artery. The inferior border is horizontal, extending from the inferior vena cava to the apex, formed mainly by the right ventricle and partly by the right atrium, and is accompanied by the right marginal branch of the right coronary artery, featuring an 'incisura cordis' near the apex. The superior border is oblique and obscured anteriorly by the aorta and pulmonary trunk, formed mainly by the left atrium and partly by the right atrium.
The sternocostal surface is large and convex, directed upward and forward, formed primarily by the right ventricle and atrium, and partly by the left ventricle and oracle. It contains the anterior right atrioventricular groove and the anterior interventricular groove. The diaphragmatic (inferior) surface is flat, with its left two-thirds formed by the left ventricle and its right one-third by the right ventricle, harboring the posterior interventricular groove. The left surface is directed upward, backward, and to the left, formed mainly by the left ventricle and partly by the left atrium and oracle.
The atrioventricular groove (coronary sulcus) demarcates the atria from the ventricles. Its anterior part is divided into right and left halves, lodging the right coronary artery trunk and the circumflex branch of the left coronary artery, respectively. The posterior part contains the coronary sinus. The interventricular groove separates the two ventricles, present anteriorly and posteriorly, lodging the anterior and posterior interventricular arteries. The interatrial groove separates the atria, being deficient anteriorly and faint posteriorly. The meeting point of the interatrial groove, coronary sulcus, and posterior interventricular groove is known as the 'crux of the heart'.
Important features include the apex being formed only by the left ventricle, the base by the left and right atria, the diaphragmatic surface by the ventricles, and the right border by the right atrium. Two-thirds of the heart lies to the left of the midline. Two-thirds of the sternocostal surface is formed by the right ventricle, and two-thirds of the diaphragmatic surface by the left ventricle. Two-thirds of the base is formed by the left atrium. For anatomical positioning, the apex should point downward, forward, and to the left, the inferior border horizontally, and the diaphragmatic surface should rest on the palm.