Internal & External Cardiac Anatomy
Explore the heart's chambers, valves, and coronary circulation — the structural foundation of every heartbeat.
Chamber Architecture & Muscle Thickness
Right Atrium receives deoxygenated blood; Right Ventricle pumps to lungs. Left Atrium receives oxygenated blood; Left Ventricle pumps to body.
The left ventricular wall is ~3× thicker because it must overcome high systemic vascular resistance.
Labeled illustration: ventricular thickness comparison (LV thick, RV thin)
- RA: systemic venous return
- RV: low-pressure pulmonary pump
- LA: pulmonary venous return
- LV: high-pressure systemic pump
The 4 Heart Valves
Ensure one-way flow. AV valves: tricuspid (right), mitral (left). Semilunar valves: pulmonic, aortic.
APETM auscultation points:
Diagram: valve locations & auscultation landmarks
Valves prevent backflow, maintaining unidirectional circulation.
Coronary Circulation
Coronary arteries supply oxygen to the myocardium. Major arteries:
- LAD: anterior wall, apex, septum
- LCx: left lateral wall
- RCA: right ventricle, inferior wall
LAD blockage is critical — supplies large portion of left ventricle (the main pump).
Coronary artery tree illustration
Key Takeaways – Section 1
- LV wall is thickest to handle systemic pressure.
- AV valves (tricuspid/mitral) separate atria from ventricles; semilunar valves guard exit.
- Coronary arteries perfuse the heart; LAD occlusion is especially dangerous.
Path of Blood Flow & Hemodynamics
Follow the journey of blood through pulmonary and systemic circuits, and understand preload, afterload, and cardiac output.
Systemic vs. Pulmonary Circulation
Systemic: Body → RA → RV → Lungs (pulmonary) → LA → LV → Body.
Vessels: vena cava, pulmonary artery, pulmonary veins, aorta.
Circulation diagram: blue = deoxygenated, red = oxygenated
Preload vs. Afterload
Preload: ventricular stretch before contraction (filling).
Afterload: resistance ventricles must overcome to eject blood.
CO = cardiac output, HR = heart rate, SV = stroke volume. Preload/afterload influence SV.
High afterload = harder to eject (e.g., hypertension).
Deoxygenated vs. Oxygenated Transitions
Gas exchange occurs in pulmonary capillaries: CO₂ out, O₂ in.
Alveoli–capillary gas exchange diagram
Deoxygenated blood (blue) becomes oxygenated (red) before returning to left atrium.
Key Takeaways – Section 2
- Pulmonary circuit oxygenates blood; systemic circuit delivers it.
- Preload = stretch; afterload = resistance. Both modulate stroke volume.
- Gas exchange transforms deoxygenated to oxygenated blood in the lungs.
Cardiac Conduction & ECG Basics
Trace the electrical pathway that times each heartbeat, and learn to read the ECG waves and common arrhythmias.
Electrical Pathway
SA node → AV node → Bundle of His → bundle branches → Purkinje fibers.
- SA node: pacemaker (60–100 bpm)
- AV node: delays signal to allow ventricular filling
- Purkinje: rapid ventricular activation
Conduction pathway illustration
Correlating Waves to Physiology
P wave: atrial depolarization. QRS: ventricular depolarization. T wave: ventricular repolarization.
Electrical activity precedes mechanical contraction.
Common Arrhythmia Basics
Normal Sinus Rhythm: regular P-QRS-T.
Atrial Fibrillation: irregularly irregular, no distinct P waves.
Ventricular Tachycardia: wide QRS, fast, often regular.
ECG comparison: NSR vs AFib vs VT
VT is potentially lethal; requires urgent assessment.
Key Takeaways – Section 3
- SA node initiates each beat; AV node delays for optimal filling.
- P = atrial depolarization, QRS = ventricular depolarization, T = repolarization.
- AFib is irregularly irregular; VT has wide QRS and is dangerous.
Clinical Pathophysiology & Nursing Assessment
Recognize heart failure, ischemic disease, and master auscultation findings for early intervention.
Heart Failure Breakdown
Heart cannot pump sufficiently to meet metabolic demands.
| Left-sided | Right-sided |
|---|---|
| Pulmonary congestion, crackles, dyspnea | JVD, peripheral edema, hepatomegaly |
Comparison illustration: pulmonary vs systemic congestion
Ischemic Heart Disease
Reduced myocardial blood supply. Angina: reversible ischemia. MI: irreversible injury.
| Biomarker | Significance |
|---|---|
| Troponin | Highly specific for myocardial injury; rises 3-6h |
| CK-MB | Less specific; useful for reinfarction |
Suspected MI requires urgent medical evaluation.
Assessment & Auscultation
S1: mitral & tricuspid closure (start of systole). S2: aortic & pulmonic closure.
S3: rapid ventricular filling (may be normal in youth). S4: atrial gallop (stiff ventricle).
Murmurs: turbulent flow across valves.
APETM auscultation diagram
Normal: S1, S2. Additional: S3, S4, murmurs.
Key Takeaways – Section 4
- Left HF → pulmonary symptoms; right HF → systemic congestion.
- Troponin is the preferred biomarker for MI; CK-MB for reinfarction.
- S1/S2 are normal; S3/S4 and murmurs may indicate pathology.