Cardiac Cycle – Model Answers (Proper Presentation
Format)
1. Cardiac Cycle (15)
Definition: Cardiac cycle is the sequence of events occurring from the beginning of one heartbeat to the
beginning of the next heartbeat.
Phases:
1. Atrial systole
2. Isovolumetric contraction
3. Rapid ejection
4. Reduced ejection
5. Isovolumetric relaxation
6. Rapid filling
7. Diastasis
Pressure Changes: LV pressure rises during isovolumetric contraction, exceeds aortic pressure during
ejection, and falls during relaxation.
Heart Sounds: S1 – closure of AV valves. S2 – closure of semilunar valves.
Diagram: Draw Wiggers diagram showing ECG, pressure, volume & heart sounds.
2. Isovolumetric Contraction (6)
Definition: Phase between AV valve closure and semilunar valve opening.
Features: Rapid rise in ventricular pressure; volume constant; all valves closed.
Significance: Generates pressure to open aortic valve.
3. Ventricular Filling (6)
Phases: Rapid filling, Diastasis, Atrial systole.
Atrial systole contributes last 20–30% of ventricular filling.
Clinical Note: Diastasis shortens first in tachycardia.
4. Atrial Systole (5)
Caused by atrial contraction; produces 'a' wave in JVP; corresponds to P wave in ECG.
5. ECG Correlation (5)
P wave – atrial depolarization → atrial systole.
QRS – ventricular depolarization → ventricular systole.
T wave – ventricular repolarization → relaxation.
6. Heart Sounds (5)
S1 – closure of mitral & tricuspid valves.
S2 – closure of aortic & pulmonary valves.
