The Heart

Focus: Human Anatomy

The heart is a fist-sized double pump in the mediastinum: the right side drives the pulmonary circuit to the lungs, the left side drives the systemic circuit to the body. This deck builds its wall, chambers, valves, muscle, and the pathway of blood. Dr. Sharilyn Rennie

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Part 1

The Heart and Its Wall

A muscular pump wrapped in a double sac, with a wall built in three layers.

Part 1 · Overview

The heart, an overview

Cardiovascular

A hollow, muscular pump in the mediastinum, resting on the diaphragm and tilted to the left.
The apex is the blunt inferior tip (down and to the left); the base is the broad superior surface where the great vessels attach.
It drives two circuits: the pulmonary circuit (right side, to the lungs and back) and the systemic circuit (left side, to the body and back).

Part 1 · Surface anatomy

The cardiac sulci

Cardiovascular

Sulcus	Location	Vessel it carries
Coronary sulcus	encircles the heart between the atria and ventricles	right coronary artery
Anterior interventricular sulcus	front surface, between the ventricles	anterior interventricular artery (LAD)
Posterior interventricular sulcus	back surface, between the ventricles	posterior interventricular artery

Sulci are fat-filled surface grooves that mark the boundaries between chambers and hold the coronary vessels.

Part 1 · Wall & sac

The heart wall and pericardium

Cardiovascular

Pericardium: a double sac. The outer fibrous pericardium protects and anchors the heart; the inner serous pericardium has a parietal layer and a visceral layer with the pericardial cavity and its lubricating fluid between them.
Heart wall, three layers: the epicardium (the visceral serous pericardium on the surface), the myocardium (the thick cardiac-muscle layer that does the pumping), and the endocardium (the smooth endothelial lining continuous with the vessels).

Cadaver heart wall labeled with the endocardium, myocardium, and epicardium (visceral pericardium). — **Heart wall layers:** endocardium, myocardium, and epicardium (visceral pericardium).

Part 1 · Clinical

Pericarditis, tamponade, and pericardiocentesis

Cardiovascular

Problem	What is going on
Acute pericarditis	most common; often viral. Chest, left arm and shoulder pain, plus a scratchy pericardial friction rub as the inflamed layers rub. Lasts about a week; treated with anti-inflammatories (ibuprofen, aspirin).
Chronic pericarditis	gradual onset; causes include cancer or tuberculosis. Pericardial fluid builds up.
Cardiac tamponade	fluid compresses the heart, so cardiac output and venous return fall, blood pressure drops, and breathing becomes difficult.
Pericardiocentesis	a needle drains the excess fluid from the pericardial sac.

The friction rub is the classic sign of pericarditis; cardiac tamponade is the emergency it can lead to.

Part 1 · Clinical

When the wall layers inflame: myocarditis and endocarditis

Cardiovascular

Condition	Definition	Signs	Treatment
Myocarditis	inflammation of the myocardium (viral, rheumatic fever, radiation, chemicals)	often none; may have fever, fatigue, chest pain, irregular heartbeat	rest, low-salt diet, ECG monitoring; usually resolves in about two weeks
Endocarditis	inflammation of the endocardium, usually the valves; most often bacterial	fever, heart murmur, irregular or rapid heartbeat, night sweats	IV antibiotics

Each wall layer has its own inflammation: peri-, myo-, and endocarditis. Endocarditis tends to attack the valves.

Part 2

Chambers, Valves, and Muscle

Four chambers, four one-way valves, and a muscle tissue found nowhere else.

Part 2 · Chambers

The four chambers

Cardiovascular

The four chambers
Chamber	Receives from	Pumps to
Right atrium	The body (venae cavae) and heart (coronary sinus)	Right ventricle
Right ventricle	Right atrium	Lungs, via the pulmonary trunk
Left atrium	Lungs, via the pulmonary veins	Left ventricle
Left ventricle	Left atrium	The body, via the aorta; its wall is the thickest

Atria are thin-walled receivers; ventricles are thick-walled pumps (left thickest). Their inner walls carry features worth knowing, shown on the next slide.

Part 2 · Chambers

Inside the chambers: features and why they are there

Cardiovascular

Inside the chambers: features and why they are there
Feature	Where	Why it is there
Interatrial septum	wall between the two atria	separates the right and left atria
Fossa ovalis	oval depression in the interatrial septum	the sealed-over remnant of the fetal foramen ovale, which let blood bypass the non-working fetal lungs; it closes at birth
Interventricular septum	thick wall between the ventricles	separates the ventricles; its muscular bulk helps drive ejection
Auricle	wrinkled flap on each atrium	adds extra atrial capacity (room to fill)
Pectinate muscles	ridges in the atria and auricles	reinforce the thin atrial walls and let the auricle expand
Trabeculae carneae	muscular ridges lining the ventricles	keep the walls from sticking together by suction so the chamber empties and refills cleanly; add strength without bulk
Moderator band	band spanning the right ventricle	carries the right bundle branch to the anterior papillary muscle, timing its contraction
Papillary muscles + chordae tendineae	project from the ventricle walls to the AV-valve cusps	tense the cords to hold the AV valves shut against ventricular pressure, preventing prolapse and backflow

Opened right atrium showing the fossa ovalis on the interatrial septum, the openings of the superior and inferior venae cavae and the coronary sinus, and pectinate muscles. — **Right atrium, opened.** Fossa ovalis (the sealed foramen ovale), vena cava and coronary sinus openings, pectinate muscles.

Opened left atrium showing the auricle, pectinate muscles, the bicuspid (mitral) valve, and the openings of the pulmonary veins. — **Left atrium, opened.** Auricle, pectinate muscles, bicuspid (mitral) valve, pulmonary vein openings.

Opened left ventricle showing chordae tendineae connecting the anterior and posterior papillary muscles to the valve cusps, and trabeculae carneae lining the wall. — **Left ventricle, opened.** Chordae tendineae, anterior and posterior papillary muscles, trabeculae carneae.

Cadaver images: University of Michigan BlueLink (B. Kathleen Alsup & Glenn M. Fox), CC BY.

Part 2 · Chambers

Wall thickness follows the workload

Cardiovascular

Chamber	Wall and lumen	Why
Atria	thin walls	low-pressure receiving chambers; they just hand blood to the ventricles
Right ventricle	thinner wall; crescent-shaped lumen	pumps a short distance to the lungs at low pressure
Left ventricle	thickest wall; circular lumen	pumps to the whole body against high pressure

Both ventricles eject the same volume per beat, but the left works against far greater resistance, so its wall is much thicker.

Part 2 · Development

Fetal structures and their adult remnants

Cardiovascular

Two model hearts showing the fetal foramen ovale becoming the fossa ovalis and the ductus arteriosus becoming the ligamentum arteriosum. — **Fetal shunts and their adult remnants:** foramen ovale to fossa ovalis, ductus arteriosus to ligamentum arteriosum.

Fetal structure	Job before birth	Adult remnant
Foramen ovale	opening in the interatrial septum; sends blood from the right atrium to the left, skipping the lungs	Fossa ovalis
Ductus arteriosus	vessel shunting blood from the pulmonary trunk to the aorta	Ligamentum arteriosum

Part 2 · Development

Congenital heart defects

Cardiovascular

Diagram comparing a normal heart with atrial septal defect, ventricular septal defect, coarctation of the aorta, and tetralogy of Fallot. — **Normal heart compared with** atrial septal defect, ventricular septal defect, coarctation, and tetralogy of Fallot.

Defect	What is wrong
Atrial septal defect (ASD)	a hole in the interatrial septum, often a foramen ovale that never sealed
Ventricular septal defect (VSD)	a hole in the interventricular septum
Tetralogy of Fallot	four defects together: a VSD, pulmonary stenosis, an overriding aorta, and right ventricular hypertrophy
Transposition of the great vessels	the aorta leaves the right ventricle and the pulmonary trunk leaves the left ventricle

Enrichment beyond the core lecture: these defects build directly on the septa and great vessels you just learned.

Part 2 · Valves

The four valves

Cardiovascular

The heart valves
Valve	Type	Between
Tricuspid	AV, 3 cusps	Right atrium and right ventricle
Mitral (bicuspid)	AV, 2 cusps	Left atrium and left ventricle
Pulmonary	Semilunar	Right ventricle and pulmonary trunk
Aortic	Semilunar	Left ventricle and aorta

Chordae tendineae tie the AV-valve cusps to papillary muscles, which hold the valves shut against ventricular pressure.

Specimen of the heart valves from above: pulmonic and aortic semilunar valves, mitral (bicuspid) and tricuspid valves. — **Specimen.** Pulmonic, aortic, mitral (bicuspid), and tricuspid valves.

Anatomical model of the heart valves: pulmonic and aortic semilunar valves, tricuspid and mitral (bicuspid) valves. — **Model.** The same four valves on an anatomical model.

Part 2 · Valves

How the valves work

Cardiovascular

Valve set	Opens when	Closes when
AV valves (tricuspid, mitral)	the atria hold more pressure than the relaxed ventricles, so blood drops into the ventricles	the ventricles contract; rising pressure pushes the cusps shut, and the papillary muscles plus chordae tendineae stop them flipping back into the atria
Semilunar valves (pulmonary, aortic)	ventricular pressure rises above the artery and blood is ejected	the ventricles relax; back-pressure fills the cup-shaped cusps and snaps them shut

Valves are passive: they open and close on pressure differences alone, keeping blood moving one way.

Part 2 · Valves

The fibrous skeleton of the heart

Cardiovascular

Function	Why it matters
Anchors the four valves	gives each valve a firm foundation
Prevents the valve openings from stretching	so they stay competent as blood passes
Anchors the cardiac muscle bundles	a point of insertion for the myocardium
Electrically insulates atria from ventricles	the impulse can only cross through the AV bundle, which times the beat

Part 2 · Conduction

Identifying the conduction system

Cardiovascular

Structure	Where to find it	What it does
SA node (pacemaker)	right atrial wall, near the opening of the superior vena cava	starts each heartbeat
AV node	interatrial septum, near the opening of the coronary sinus	the gateway from the atria to the ventricles
AV bundle (bundle of His)	pierces the fibrous skeleton into the interventricular septum	the only electrical bridge across the insulating skeleton
Right and left bundle branches	run down the interventricular septum toward the apex	carry the impulse to each ventricle
Purkinje fibers	spread up through the ventricular walls from the apex	hand the impulse to the ventricular muscle
Moderator band	crosses the right ventricle to the anterior papillary muscle	carries the right bundle branch (the feature from the chambers slide)

Because the fibrous skeleton insulates the atria from the ventricles, the AV bundle is the only path the impulse can take. That is why conduction can be traced as an anatomical pathway, and why the atria always contract just before the ventricles. The electrophysiology (rates, action potentials, ECG) belongs to the physiology deck.

Part 2 · Valves

Valve disorders

Cardiovascular

Disorder	What happens
Stenosis	a valve opening narrows and restricts flow (for example mitral stenosis, aortic stenosis)
Insufficiency (incompetence)	a valve fails to close fully, so blood leaks backward
Mitral valve prolapse	a cusp balloons into the left atrium during contraction; common (about 30 percent), usually not serious
Rheumatic fever	a post-strep immune reaction that can scar the valves
Valve replacement	human, pig, or mechanical valve; the aortic valve is replaced most often

Part 2 · Cardiac muscle

Cardiac muscle and the intercalated disc

Histology

The myocardium is cardiac muscle, a tissue found nowhere else: striated, branched, with one central nucleus and many mitochondria.
Cells join end to end at intercalated discs, which hold desmosomes (mechanical glue) and gap junctions (let the impulse pass cell to cell).
Because the gap junctions link the cells electrically, the muscle behaves as a functional syncytium: the whole chamber contracts as a unit. It is involuntary and autorhythmic.

Light micrograph of cardiac muscle: short branched fibres with central nuclei, faint striations, and intercalated discs joining the cells end to end. — **Cardiac muscle (H&E):** short branched fibres, central nuclei, striations, joined end to end by intercalated discs.

Part 3

The Pathway of Blood

Follow one drop through the right heart, the lungs, and the left heart, then meet the great vessels and the heart's own supply.

Part 3 · Blood pathway

Trace a drop of blood

Cardiovascular

Right heart = to the lungs (pulmonary); left heart = to the body (systemic). The AV valves (tricuspid, mitral) guard the atrium-to-ventricle doors; the semilunar valves (pulmonary, aortic) guard the exits.

Part 3 · Great vessels

The great vessels

Cardiovascular

Superior and inferior venae cavae: return oxygen-poor blood from the upper and lower body to the right atrium.
Pulmonary trunk: carries blood from the right ventricle to the lungs, splitting into right and left pulmonary arteries.
Pulmonary veins (four): return oxygen-rich blood from the lungs to the left atrium.
Aorta: the largest artery, carrying oxygen-rich blood from the left ventricle to the body.

Anatomical model of the heart and great vessels, labeled: left brachiocephalic vein, superior vena cava, right brachiocephalic trunk with right common carotid and right subclavian arteries, aorta, and pulmonary trunk. — **Model.** Brachiocephalic vein and SVC, brachiocephalic trunk (to right common carotid and subclavian), aorta, and pulmonary trunk.

Cadaver specimen of the heart and great vessels, labeled with the same vessels: left brachiocephalic vein, superior vena cava, right brachiocephalic trunk, right common carotid and subclavian arteries, aorta, and pulmonary trunk. — **Cadaver specimen.** The same great vessels in a real heart.

Cadaver image: University of Michigan BlueLink (B. Kathleen Alsup & Glenn M. Fox).

Part 3 · Coronary supply

The coronary circulation

Cardiovascular

The heart wall feeds itself: aorta -> coronary arteries -> myocardial capillaries -> cardiac veins -> coronary sinus -> right atrium.

The two coronary arteries
Artery	Main branches	Supplies
Right coronary (RCA)	Right marginal; posterior interventricular (PDA)	Right atrium and ventricle, posterior septum, and usually the SA and AV nodes
Left coronary (LCA)	Anterior interventricular (LAD); circumflex; left marginal	Most of the left atrium and ventricle and the anterior septum

The cardiac veins drain into the coronary sinus on the posterior heart, which empties into the right atrium: the great cardiac vein (runs with the LAD), the middle cardiac vein (with the PDA), and the small cardiac vein (with the right marginal artery).

Blocking a coronary artery starves the myocardium it feeds, the basis of a heart attack (myocardial infarction). (Clinical, beyond the notes.)

Part 3 · Coronary supply

Coronary veins, the coronary sinus, and anastomoses

Cardiovascular

Cardiac vein	Runs in	Drains
Great cardiac vein	anterior interventricular sulcus	region supplied by the left coronary artery
Middle cardiac vein	posterior interventricular sulcus	region supplied by the posterior interventricular artery
Small cardiac vein	coronary sulcus	right atrium and right ventricle
Anterior cardiac veins	(open directly into the right atrium)	right ventricle

Most cardiac veins empty into the coronary sinus on the posterior heart, which drains into the right atrium. Anastomoses are artery-to-artery connections that give collateral (backup) routes if a vessel is blocked.

Part 4

Check Your Understanding

From recall to reasoning, then the key takeaways.

Part 4 · Recall (DOK 1)

Name the valve

Practice

Depth of Knowledge 1 · Recall

Which valve sits between the left atrium and the left ventricle?

Part 4 · Skill / concept (DOK 2)

Apply the structure

Practice

Depth of Knowledge 2 · Skill / concept

Why is the wall of the left ventricle the thickest of the four chambers?

Part 4 · Strategic reasoning (DOK 3)

Reason it through

Practice

Depth of Knowledge 3 · Strategic reasoning

If a papillary muscle ruptures during a heart attack, why does blood leak backward through the AV valve?

Wrap-up

Key takeaways

Summary

The heart wall = epicardium, myocardium, endocardium, inside the pericardium.
Four chambers: atria receive, ventricles pump; the left ventricle is thickest.
Four valves: tricuspid and mitral (AV) guard the atria; pulmonary and aortic (semilunar) guard the exits; chordae and papillary muscles hold the AV valves shut.
Cardiac muscle is striated and branched with intercalated discs (gap junctions) that make it a functional syncytium.
Blood: RA -> tricuspid -> RV -> pulmonary valve -> lungs -> LA -> mitral -> LV -> aortic valve -> body.
The coronary arteries feed the heart; blocking one causes a heart attack.

Acknowledgment

With thanks

Cardiovascular

A special thank you to BlueLink Anatomy, University of Michigan Medical School, for the cadaver and anatomical image materials that appear throughout this deck.

Used with appreciation for their generosity in sharing open anatomical teaching resources.

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Take it with you

Cardiovascular

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