[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Histology](https://durgical.com/en/histology/) › [Cardiovascular system](https://durgical.com/en/histology/#a-cardiovascular) › The heart wall, valves and conduction tissue [Histology](https://durgical.com/en/histology/) · [Cardiovascular system](https://durgical.com/en/histology/#a-cardiovascular) # The heart wall, valves and conduction tissue - Organ The heart wall has three layers: a thin inner lining, a thick muscle and an outer coat. Valves are flaps of lining around a fibrous core. Updated 2026-11-01 **See it in 3D:** [Pericardium](https://durgical.com/en/anatomy/pericardium/) · [Mitral anterior leaflet](https://durgical.com/en/anatomy/anterior-leaflet-of-left-atrioventricular-valve/) · [Sinoatrial (SA) node](https://durgical.com/en/anatomy/sinuatrial-node/) · [Atrioventricular (AV) node](https://durgical.com/en/anatomy/atrioventricular-node/) · [Bundle of His](https://durgical.com/en/anatomy/atrioventricular-bundle/) ## Key points - Endocardium, myocardium, epicardium; the left ventricular myocardium is the thickest. - Cardiomyocytes: branched, one or two central nuclei, striated, joined by intercalated discs (desmosomes plus gap junctions). - Purkinje fibres: large pale cells rich in glycogen with few myofibrils, under the endocardium. - SA node in the right atrial wall near the superior vena cava; AV node in the lower interatrial septum; the AV delay lets the ventricles fill. - Valves have a fibrous core covered by endothelium and few or no vessels, so infection settles there easily. - Rheumatic heart disease, still common in Latin America, most often scars the mitral valve. ## What it is From inside out the heart wall has endocardium (endothelium and subendothelial tissue), myocardium (cardiac muscle, the thickest layer) and epicardium (the visceral layer of the serous pericardium, with fat and coronary vessels). Valves are folds of endocardium around a dense connective-tissue core. Specialised cardiac muscle cells form the conduction system, from the sinoatrial node to the Purkinje fibres. ## Structure - Endocardium: endothelium on loose connective tissue; the subendocardial layer carries vessels, nerves and Purkinje fibres. - Myocardium: spiralling bundles of cardiomyocytes, rich capillaries, little interstitial tissue. - Epicardium: mesothelium with fat in which the coronary arteries run. - Cardiac skeleton: rings of dense connective tissue around the valves that also insulate atria from ventricles electrically. - Atrioventricular valves are tethered by chordae tendineae to papillary muscles; semilunar valves have none. ## Function - Gap junctions let the impulse spread so the heart contracts as one unit. - Atrial cardiomyocytes contain granules of atrial natriuretic peptide, released when the atria stretch. ## Clinical notes - Myocardial infarction: coagulative necrosis, then neutrophils, macrophages and finally a collagen scar; the muscle does not regenerate. - Rheumatic carditis: Aschoff nodules and fibrosis that thicken and fuse the mitral leaflets. - Chagas cardiomyopathy (Trypanosoma cruzi): chronic myocarditis with fibrosis that damages the conduction system. - Infective endocarditis forms vegetations on the largely avascular valve surface. ## Memory aid Read the wall like a sandwich: Endo is the inner slice of bread, Myo the thick filling, Epi the outer slice with the coronary sauce. ## Test yourself Think of the answer, then tap the question to see it. ## Which structures join cardiomyocytes end to end and what do they contain? Intercalated discs, with desmosomes (and adherens junctions) for mechanical coupling and gap junctions for electrical coupling. ## How are Purkinje fibres recognised on H&E? They are large, pale cells under the endocardium, rich in glycogen and with few myofibrils at the periphery. ## Why does the impulse pause at the AV node? Nodal cells are small and poorly coupled, so conduction slows; the delay lets the atria finish filling the ventricles. ## What layer of the heart wall is the epicardium part of? It is the visceral layer of the serous pericardium: mesothelium with fat that carries the coronary vessels. [Add to my cards (4)](https://durgical.app/estudiar/?add=/en/histology/the-heart-wall-valves-and-conduction-tissue/) ## See it in 3D The structures of Durgical's 3D anatomy where it is found. - [Pericardium](https://durgical.com/en/anatomy/pericardium/) - [Mitral anterior leaflet](https://durgical.com/en/anatomy/anterior-leaflet-of-left-atrioventricular-valve/) - [Sinoatrial (SA) node](https://durgical.com/en/anatomy/sinuatrial-node/) - [Atrioventricular (AV) node](https://durgical.com/en/anatomy/atrioventricular-node/) - [Bundle of His](https://durgical.com/en/anatomy/atrioventricular-bundle/) ## Related - [Cardiac muscle: intercalated discs](https://durgical.com/en/histology/cardiac-muscle-intercalated-discs/) - [Blood vessels: artery, vein and capillary layers](https://durgical.com/en/histology/blood-vessels-artery-vein-and-capillary-layers/) - [Serous membranes: pleura and peritoneum](https://durgical.com/en/histology/serous-membranes-pleura-and-peritoneum/) ## Related conditions - [Rheumatic heart disease](https://durgical.com/en/conditions/rheumatic-heart-disease/) - [Chagas cardiomyopathy](https://durgical.com/en/conditions/chagas-cardiomyopathy/) - [Infective endocarditis](https://durgical.com/en/conditions/infective-endocarditis/) - [Atrioventricular (heart) block](https://durgical.com/en/conditions/atrioventricular-block/) - [Atrial fibrillation](https://durgical.com/en/conditions/atrial-fibrillation/) ## Microorganisms - [Trypanosoma cruzi](https://durgical.com/en/microbiology/trypanosoma-cruzi/) - [Streptococcus pyogenes](https://durgical.com/en/microbiology/streptococcus-pyogenes/) [← All of histology](https://durgical.com/en/histology/) Educational content on normal microscopic structure and its clinical relevance; no substitute for studying slides or for a health professional's advice. Sources: [19.1 Heart Anatomy - Anatomy and Physiology 2e | OpenStax](https://openstax.org/books/anatomy-and-physiology-2e/pages/19-1-heart-anatomy) (OpenStax, Rice University, 2022); [19.2 Cardiac Muscle and Electrical Activity - Anatomy and Physiology 2e | OpenStax](https://openstax.org/books/anatomy-and-physiology-2e/pages/19-2-cardiac-muscle-and-electrical-activity) (OpenStax, Rice University, 2022). ## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake Representative model, for educational purposes only. --- Source: https://durgical.com/en/histology/the-heart-wall-valves-and-conduction-tissue/ License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/histology/the-heart-wall-valves-and-conduction-tissue/