Anatomy of the Right Atrium

The fossa ovalis is a shallow, oval depression in the atrial septum that indicates the site of the foramen ovale in the fetus.

The anulus ovalis is a ridge that forms the upper margin of the fossa ovalis and is derived from the lower edge of the septum secundum.

The openings in the right atrium are the SVC opening, IVC opening, coronary sinus opening, and right atrioventricular (or tricuspid) opening.

The left atrium forms the greater part of the base of the heart, lies behind the right atrium, and lies anterior to the oblique pericardial sinus and esophagus.

The openings in the left atrium are the four pulmonary veins and the left atrioventricular (or mitral) opening.

The atrioventricular sulcus is directed downward, forward, and to the left, and lies at the level of the 5th left intercostal space, 9 cm from the midline.

The two parts of the right atrium are the smooth-walled part posterior to the crista terminalis and the rough-walled part anterior to the crista terminalis. The smooth-walled part is derived from the sinus venosus, while the rough-walled part is derived from the primitive atrium.

The sulcus terminalis is a shallow, vertical groove at the junction between the right atrium and the right auricle, corresponding to the crista terminalis inside the right atrium. It is significant because it is near the SA node.

The right border is formed by the right atrium, the inferior border is formed by the right ventricle and partly by the right atrium, and the left border is formed by the left ventricle and part of the left auricle.

The pulmonary valve lies posterior to the sternal end of the 3rd left costal cartilage.

The atrioventricular openings are the openings between the atria and ventricles, and they are significant because they allow blood to flow between the atria and ventricles.

The pericardium serves as a lubricated container that restricts excessive movements of the heart. It consists of two layers: the fibrous pericardium (outermost) and the serous pericardium (inner layer), which has parietal and visceral layers. These layers enable the heart to move smoothly and facilitate its function.

The transverse pericardial sinus is located between the aorta and pulmonary trunk, and it lies posterior to the aorta and pulmonary trunk. It is significant because it forms a passage for the great vessels to pass through.

The surfaces of the heart are the sternocostal (anterior), diaphragmatic (inferior), base (posterior), and apex. The sternocostal surface is formed by the right atrium and right ventricle, the diaphragmatic surface is formed by the right ventricle and left ventricle, the base is formed by the left atrium, and the apex is formed by the left ventricle.

The borders of the heart are the superior, right, inferior, and left borders. The superior border demarcates the heart from the great vessels, the right border demarcates the right atrium and right ventricle, the inferior border demarcates the heart from the diaphragm, and the left border demarcates the left atrium and left ventricle.

The atrioventricular openings are the passages that connect the atria to the ventricles. The right atrioventricular opening connects the right atrium to the right ventricle, and the left atrioventricular opening connects the left atrium to the left ventricle.

The atrioventricular sulcus separates the atria from the ventricles, and the interventricular sulcus separates the right ventricle from the left ventricle. These sulci are significant because they demarcate the boundaries between the atria and ventricles and facilitate the flow of blood.