Chapter 57: Heart Anatomy

Key reflections in the serous membrane create spaces like the oblique pericardial sinus and the transverse pericardial sinus. Clinically, excessive fluid buildup in the narrow pericardial cavity leads to cardiac tamponade, a condition requiring pericardiocentesis. The heart itself is positioned obliquely, resembling a pyramid with surfaces including the anterior (sternocostal) and inferior (diaphragmatic), emphasizing the need for understanding its true in vivo orientation where the left atrium is posterior and the diaphragmatic surface is inferior. Functionally, the heart is an asymmetric pair of pumps: the right heart manages low-pressure pulmonary circulation, receiving systemic venous blood into the right atrium which contains important landmarks like the crista terminalis and the Triangle of Koch. The right ventricle is thin-walled and crescentic, ejecting blood through the pulmonary valve via the conus arteriosus (infundibulum). The thick-walled left ventricle drives the high-pressure systemic circulation, receiving blood from the left atrium through the mitral valve and ejecting it through the aortic valve. Valve competence is maintained by structures such as chordae tendineae and papillary muscles. Crucial support and electrical separation are provided by the fibrous skeleton of the heart, particularly strong at the central fibrous body, which is the intersection of the mitral, tricuspid, and aortic valve planes. The electrical excitation begins at the primary pacemaker, the sinuatrial node, located near the superior vena cava and the sulcus terminalis. The impulse is briefly delayed at the atrioventricular node before traveling down the atrioventricular bundle (of His) into the specialized ventricular conduction pathways. Arterial supply is provided by the right coronary artery (RCA) and the left coronary artery (LCA), which arise from the aortic sinuses and run in the atrioventricular sulci, with variations like coronary dominance (RCA is dominant in 60%) and myocardial bridges affecting flow. Venous return is collected primarily by the coronary sinus, draining into the right atrium, supplemented by vessels like the anterior cardiac veins and the minute smallest cardiac (Thebesian) veins. Finally, the heart's rate and force are modulated by the autonomic nervous system via the cardiac plexus.