Cardiac Physiology for UPSC CMS: Cardiac Cycle, ECG, Heart Sounds and Hemodynamics

Cardiac Cycle

Atrial systole: Atria contract, push remaining blood into ventricles (80% already filled passively). "A" wave.

Isovolumetric contraction: AV valves close, ventricles contract. S1 produced. Pressure rises to aortic pressure.

Rapid ejection: Aortic valve opens. Blood ejected rapidly.
Reduced ejection: Ejection continues slowly.

Isovolumetric relaxation: Aortic valve closes, S2 produced. Pressure falls.

Rapid filling: AV valves open, blood rushes in.
Diastasis: Slow filling phase.

ECG Waves

P wave = atrial depolarization. PR interval = AV conduction. QRS = ventricular depolarization. ST segment = ventricular plateau. T wave = ventricular repolarization.

Frank-Starling Mechanism

Increased preload -> increased stretch -> increased force of contraction. Explains how heart adjusts output to venous return.