Heart is a blood pumping muscular organ of middle mediastinum having 3 layers (outer epicardium, middle mesocardium and innermost endocardium) covered by fibrous pericardial sheath and having four chambers, two on the left (left atrium and left ventricle) and two on the right (right atrium and right ventricle).
Pericardium along with heart also cover the mediastinal great vessels. The outer wall of pericardial sac consists of outer fibrous and inner serosa. Histologically fibrous is fibrocollagenous tissue while serosa is composed of mesothelial cells. Laterally, pericardium forms medial walls of pleural space. Inferiorly, pericardium is the superior surface of central tendon of diaphragm. Anteriorly pericardium is loosely joined to xiphoid process and sternal manubrium by ligamentous structures.
It has four basic parts-1. left atrial appendage 2. the vestibule and 3. the venous component. It is separated from right atrium by the septum- interatrial septum. Unlike of the right atrium, the pectinate muscles are confined within the appendage and do not extend around the vestibule. Because of the the anchorage by the four pulmonary veins, the left atrium is fixed posteriorly.
It has mainly three components- 1. the inlet, 2. the trabecular and 3. the outlet portion. The inlet portion contains the mitral valve and its supporting tension apparatus. The outlet portion supports the aortic valve. The septal surface of outflow tract is characteristically smooth, and down this smooth surface runs the fanlike left bundle. The landmark for descent of left bundle branch is the membranous septum immediately beneath the commissure between right coronary and non coronary leaflets of the aortic valves.
Right atrium like that of the left atrium has also three parts – 1. the appendage, 2. vestibule, 3. venous component.
Externally the junction of the right atrial appendage and the venous component is marked by a groove called the terminal groove. The appendage has pectinate muscles. The constant feature of the morphologic right atrium is that the pectinate muscles of appendage extend all the way around the parietal margins of the AV junction. Sinus node is a spindle shaped structure that lies within the terminal groove in a sub pericardial portion. Sinus node artery usually courses through the anterior interatrial groove towards the superior cavoatrial junction. From surgical point of view the entire superior cavoatrial junction is a potential surgical danger area.
Right ventricle has three parts- 1. inlet, 2. trabecular and 3. the outlet portion. The inlet portion contains tricuspid valve and its tension apparatus. A distinguishing feature of the tricuspid valve is the direct septal attachment of its septal leaflets. Trabecular portion is a supra ventricular crest portion of right ventricle is the prominent muscular shelf separating the tricuspid and pulmonary valves. The outlet portion is a complete muscular structure, the infundibulum, which supports leaflets of the pulmonary valve. Another important feature of the right ventricle is a muscular column called trabeculae septomarginalis. This trabeculation has a body which divides superiorly into anterior and posterior limbs. The anterior limb runs up into the infundibulum and supports the leaflets of pulmonary valve. The posterior limb extends backward beneath the inter ventricular membranous septum to run into the inlet component of ventricle. The medial papillary muscle arises from this posterior limb.