Cardiac Anatomy
The heart is a hollow, muscular organ in the mediastinum. Four chambers: right atrium (RA), right ventricle (RV), left atrium (LA), left ventricle (LV). Four valves: tricuspid (RA→RV), pulmonic (RV→PA), mitral (LA→LV), aortic (LV→aorta). LV wall is thickest due to systemic resistance.
The Cardiac Cycle
Systole: ventricular contraction and ejection. Diastole: ventricular relaxation and filling. Normal ejection fraction (EF): 55–70%. S1 ("lub") = AV valve closure at onset of systole. S2 ("dub") = semilunar valve closure at end of systole.
Electrical Conduction System
SA node (pacemaker, 60–100 bpm) → AV node (delays 0.1 sec) → Bundle of His → Bundle Branches → Purkinje fibers → ventricular myocardium. P wave = atrial depolarization. QRS = ventricular depolarization. T wave = ventricular repolarization.
Cardiac Output
CO = Heart Rate × Stroke Volume. Normal CO: 4–8 L/min. Factors affecting SV: preload (venous return), afterload (resistance), contractility (muscle strength). Frank-Starling Law: within limits, increased stretch → increased contraction force.
Important Notes
- Left-sided HF causes pulmonary symptoms (crackles, dyspnea); right-sided causes systemic congestion (edema, JVD).
- The AV node is the only normal electrical bridge between atria and ventricles.
Clinical Tips
- "All People Eat Too Much" = anatomical valve order (Aortic, Pulmonic, Epstein/tricuspid, Too/mitral).
- Listen to S1 best at apex; S2 best at base (aortic/pulmonic areas).
Summary
The heart is a precisely engineered pump. Understanding anatomy, electrical conduction, and mechanical cycle is foundational for ECG interpretation, recognizing heart failure, and cardiac nursing care.
