Cardiac event at the end of isometric relaxation phase:

Corresponds to peak of C wave in JVP

Aortic valve closure occurs in which part of cardiac cycle?

Beginning of isovolumetric relaxation

Beginning of isovolumetric contraction

During rapid ventricular filling

Beginning of ventricular ejection

All of the following statements about the third heart sound (S3) are true, except:

Seen in Constrictive Pericarditis

Seen in Atrial Septal Defect (ASD)

Seen in Ventricular Septal Defect (VSD)

Occurs due to rapid filling of the ventricles during early diastole.

What is the correct sequence of phases that follows isovolumic contraction in the cardiac cycle?

Ejection, Isovolumic relaxation

Atrial systole, Isovolumic contraction

Which of the following is correct about the pressure volume loop of left ventricle?

1 to 2 indicates isovolumetric relaxation

2 to 3 indicates ventricular diastole

The recording of cardiac cycle is drawn below. Which of the following is correct about $X$ and $Y$ shown in the image?

$X=$ Pre-ejection period and $Y=$ LV ejection time

$X=$ Pre-ejection period and $Y=$ Electromechanical systole

$X=$ LV ejection time and $Y=$ Pre-ejection period

$X=$ Electromechanical systole and $Y=$ LV ejection time

Which of the following is correct about the 'X' marking in Arterial Waveform?

Rapid filling of left ventricle

Cardiac Cycle for INI-CET: High-Yield Physiology Lessons

Cardiac Cycle Overview - Heart's Rhythm Roadmap

Sequence of mechanical and electrical events during one complete heartbeat.
Duration: Typically 0.8 seconds at 75 beats per minute (bpm).
- Calculated as: $Cardiac Cycle Duration (s) = 60 / Heart Rate (bpm)$.
Two Major Phases:
- Systole: Ventricular contraction and ejection.
- Diastole: Ventricular relaxation and filling.

⭐ With increased heart rate, the cardiac cycle shortens. This reduction is disproportionately greater for diastole compared to systole.

Mechanical Events: Systole - The Big Squeeze

Ventricular depolarization (QRS complex) initiates contraction. Duration: ~0.27s-0.35s.
Comprises three phases:
- Isovolumetric Contraction: Ventricles contract, all valves closed. Pressure ↑↑, volume constant. S1 sound.
- Rapid Ejection: Semilunar valves open. Ventricular pressure > great arteries. Max outflow. Volume ↓↓.
- Reduced Ejection: Ejection slows. Ventricular pressure starts to ↓. Volume ↓.
End-Systolic Volume (ESV): ~50ml. Stroke Volume (SV) = $EDV - ESV$.

Cardiac Cycle: Pressure, Volume, ECG, and Heart Sounds

⭐ During isovolumetric contraction, all heart valves are closed, ventricular pressure rises sharply, and ventricular volume remains unchanged, producing the S1 heart sound.

Mechanical Events: Diastole - Relax & Refill

Ventricular relaxation and filling. Duration: ~0.5s (at 75bpm).
Phases:
- Isovolumetric Relaxation: All valves closed. Vent. pressure ↓. Volume constant (ESV). S2 sound (semilunar valve closure).
- Rapid Filling: AV valves open. Vent. pressure < Atrial pressure. Vent. volume ↑ rapidly.
- Reduced Filling (Diastasis): Slow ventricular filling. Longest phase.
- Atrial Systole ('Atrial Kick'): Atrial contraction. Adds last 20-30% to ventricular filling (EDV ~120ml).

Cardiac Cycle Phases and Valve Status

⭐ The 'atrial kick' significantly contributes to ventricular filling, especially in conditions like hypertension or tachycardia where passive filling time is reduced.

Pressure-Volume Dynamics - Wiggers & Loops

Wiggers Diagram: Synchronizes ECG, heart sounds, and pressure/volume changes in atria, ventricles, and aorta during one cardiac cycle.
Pressure-Volume (PV) Loop: Plots ventricular pressure vs. volume.
- Phases: Ventricular Filling, Isovolumetric Contraction, Ejection, Isovolumetric Relaxation.
- Stroke Volume (SV) = $EDV - ESV$ (loop width).
- Ejection Fraction (EF) = $(SV / EDV) * 100%$; Normal >55%.

⭐ The width of the Pressure-Volume loop represents Stroke Volume; its area approximates ventricular stroke work.

Heart Sounds - Cardiac Symphony

Sound	Cause	Timing	Characteristics	Clinical Significance
S1	AV valve closure (M1, T1)	Start Systole	'LUB' 📌	Loud: MS, ↑CO. Soft: MR, long PR.
S2	Semilunar valve closure (A2, P2)	End Systole	'DUB' 📌	A2 before P2.
S3	Rapid ventricular filling	Early Diastole	Low pitch, 'Kentucky' 📌	Normal <40 yrs; Path: LVF, MR.
S4	Atrial contraction (stiff ventricle)	Late Diastole	Low pitch, 'Tennessee' 📌	Path: LVH, AS, HOCM, acute MI.

High‑Yield Points - ⚡ Biggest Takeaways

Cardiac cycle duration is 0.8s (at 75 bpm); systole 0.3s, diastole 0.5s.

S1 (lub): AV valve closure (mitral/tricuspid); marks start of ventricular systole.

S2 (dub): Semilunar valve closure (aortic/pulmonary); marks end of ventricular systole.

Isovolumetric phases (contraction & relaxation): All valves closed; ventricular volume constant.

Majority of ventricular filling is passive during early diastole (rapid inflow).

Dicrotic notch in aortic pressure curve signifies aortic valve closure and start of diastole.

Atrial systole contributes the final 20-30% of ventricular filling ("atrial kick").

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Cardiac Cycle