Cardiac cycle

2026

📘 Cardiac Cycle - Complete Exam Notes

🖇 I. Introduction & Assessment Methods

📌 Assessment of Cardiac Cycle

• Three main methods:
• 1. Assessment via device
  2. Assessment via artery
  3. Assessment via vein

📌 Lecture Coverage

• Cardiac Cycle
• Heart anatomy (Atrium and Ventricle)
• Heart Sounds (covered in practicals)
• ECG (Electrocardiography)

🟣 Three Methods to Assess Cardiac Cycle (Exam Point)

🚨 Assessment Methods:

1. Recording/Assessment of Jugular Venous Pressure (JVP)
2. Recording/Assessment of Arterial Pulsation (taken in practicals)
3. Recording of ECG (Electrocardiography) (taken in theory and practicals)

📌 Note

• Heart's electrical and mechanical processes must be assessed
• JVP assessment potentially not included in standard textbook

🖇 II. Cardiac Structure & Cycle Overview

📌 Cardiac Anatomy Components

• Right and Left Atrium
• Right and Left Ventricle
• Aorta
• Pulmonary Artery
• Aortic Valve
• Superior Vena Cava
• Inferior Vena Cava
• Four pulmonary veins

🟣 Cardiac Cycle Definition

📌 Definition

• The cycle or sequence of events that occurs during one heartbeat
• Encompasses Systole and Diastole

📌 Phases Involved

• Atrial Systole
• Atrial Diastole
• Ventricular Systole
• Ventricular Diastole

📌 Note on Atrial Diastole

• Many books omit Atrial Diastole
• Lecturer includes it because Atrium must relax (Diastole) following contraction (Systole)

🖇 III. Duration & Timing of Cardiac Cycle

📌 Normal Heart Rate

• 70 or 75 beats per minute
• Normal range: 60-90 beats per minute
• Average: 75 beats per minute

🚨 Heart Rate Measurement (Exam Point)

• Must be measured when patient is at rest
• In normal condition (e.g., sitting for five minutes)
• Exercise or stress increase the rate

🟣 Total Duration (Exam Point)

🚨 Total Duration of Cardiac Cycle: 0.8 seconds

📌 Phase Durations

• Atrial Systole: 0.15 seconds (some sources: 0.1 seconds)
• Atrial Diastole: 0.65 seconds (some sources: 0.7 seconds)

🟣 Overlap of Phases

📌 Phase Relationships

• Ventricular Systole and majority of Ventricular Diastole occur during Atrial Diastole
• Smaller remaining portion of Ventricular Diastole occurs during Atrial Systole
• Atrium and Ventricle empty together and fill together

🖇 IV. Detailed Phases of Ventricular Systole & Diastole

🟣 Ventricular Systole (Total Duration: 0.3 seconds)

📌 Three Phases:

1. Isometric Contraction Phase: 0.05 seconds
2. Maximum Ejection Phase: 0.15 seconds
3. Reduced Ejection Phase: 0.10 seconds

🟣 Ventricular Diastole (Total Duration: 0.5 seconds)

📌 Four Phases:

1. Protodiastolic Phase (transition)
2. Isometric Relaxation Phase: 0.05 seconds
3. Rapid Filling Phase / Maximum Filling Phase: 0.15 seconds
4. Reduced Filling Phase: 0.20 seconds

• Some sources include Last Rapid Filling Phase

🟣 Correspondence Between Systole & Diastole

📌 Key Difference

• Phases share similar names
• Systole: involves Contraction and Ejection (pumping blood)
• Diastole: involves Relaxation and Filling (receiving blood)

🖇 V. Essential Elements for Cardiac Cycle Analysis (Exam Point)

🚨 Seven Specific Items Required for Every Phase (Exam Point):

1. Duration of the phase
2. Intra-Atrial Pressure
3. Intra-Ventricular Pressure
4. Aortic/Pulmonary Pressure
5. Volume in the Ventricle
6. ECG changes
7. Heart Sounds heard

🚨 Study Advice (Exam Point)

• Construct a large table containing these seven parameters across all phases of Cardiac Cycle

🖇 VI. DETAILED PHASE ANALYSIS: ATRIAL SYSTOLE

📌 Valve Status

• AV Valves (Mitral and Tricuspid): OPEN
• Semilunar Valves: CLOSED

🟣 Filling Mechanism

📌 Blood Entry

• Approximately 80% of ventricular filling occurs passively
• Atrial Systole causes final 20% of blood to enter Ventricle

🟣 Pressure & Volume Changes

📌 Ventricular Pressure (Pv)

• Initially increases (due to incoming blood)
• Then decreases toward end (due to elastic stretching of Ventricle - acts like balloon)

📌 Ventricular Volume (Vv)

• Continuously INCREASES (blood entering, cannot leave)

📌 Atrial Pressure (Pa)

• Initially decreases
• Final contraction slightly increases pressure

📌 Aortic/Pulmonary Pressure (Ao/Pao)

• DECREASES (Semilunar Valves closed, blood flowing to peripheral circulation)

🟣 ECG Changes

📌 P Wave

• Starts about 0.02 seconds before phase begins
• Most of P wave occurs during Atrial Systole

📌 P Wave Meanings:

• In ECG: P wave = Atrial Depolarization (electrical change)
• In Cardiac Cycle: P wave = Atrial Systole (mechanical change/contraction)

🟣 Heart Sound

📌 Fourth Heart Sound (S4)

• Heard during this phase
• Pathological Heart Sound
• Typically NOT audible with stethoscope

🖇 VII. DETAILED PHASE ANALYSIS: VENTRICULAR SYSTOLE (0.3 sec)

🟣 A. Isometric Contraction Phase (0.05 sec)

📌 Valve Status

• Ventricular pressure rises → closes two AV Valves
• Semilunar Valves already closed
• ALL FOUR VALVES ARE CLOSED

🚨 Isometric Phase Rule (Exam Point)

• Any "Isometric" phase means all valves are closed
• Ventricle acts as closed chamber

Pressure & Volume Changes

📌 Ventricular Volume (Vv)

• CONSTANT (no blood entering or leaving)

📌 Ventricular Pressure (Pv)

• Intra-Ventricular Pressure INCREASES sharply (contraction against closed valves)

📌 Atrial Pressure (Pa)

• Increases slightly
• Causes C wave in JVP
• Due to pressure forcing AV valves to bulge into Atrium

📌 Aortic/Pulmonary Pressure (Ao/Pao)

• Continues to DECREASE

Heart Sound & ECG

📌 Heart Sound

• First Heart Sound (S1) heard
• Caused by closure of AV Valves

📌 ECG

• Q Wave begins to appear
• QRS Complex signifies Ventricular Depolarization

🟣 B. Maximum Ejection Phase (0.15 sec)

📌 Valve Status

• Ventricular pressure exceeds Aortic/Pulmonary pressure
• Two Semilunar Valves OPEN
• AV Valves remain closed

📌 Blood Movement

• Rapid blood ejection into Aorta and Pulmonary Artery

Pressure & Volume Changes

📌 Ventricular Pressure (Pv)

• Reaches peak:
• • Left Ventricle: 120 mmHg
  • Right Ventricle: 25 mmHg
• Then begins to decrease

📌 Ventricular Volume (Vv)

• DECREASES rapidly

📌 Aortic/Pulmonary Pressure (Ao/Pao)

• INCREASES (due to incoming blood volume)

ECG

📌 QRS Complex Completion

• R and S waves complete the QRS Complex

🟣 C. Reduced Ejection Phase (0.10 sec)

📌 Valve Status

• Semilunar Valves remain OPEN until very end of ejection

📌 Blood Movement

• Ejection continues but slows down significantly

Pressure & Volume Changes

📌 General Trend

• Ventricular volume: DECREASES
• Ventricular pressure: DECREASES
• Atrial pressure: DECREASES

📌 Aortic Pressure (Ao/Pao) - Conflicting Views

• Some say it decreases (lecturer favored): peripheral outflow exceeds ventricular inflow
• Others say it increases: blood still entering vessel

Heart Sound & ECG

📌 Heart Sound

• No specific new sound heard

📌 ECG

• Peak of T wave starts to form

🟠 Clinical Note

• Backward flow of blood from Aorta/Pulmonary Artery into Ventricle = pathological (regurgitation)

🖇 VIII. DETAILED PHASE ANALYSIS: VENTRICULAR DIASTOLE (0.5 sec)

🟣 A. Protodiastolic Phase (Transition)

📌 Nature

• Transition phase between Ventricular Systole and Diastole

📌 Valve Status

• All valves briefly CLOSED

📌 Classification

• Lecturer places this phase under Ventricular Diastole

🟣 B. Isometric Relaxation Phase (0.05 sec)

📌 Definition

• Ventricular relaxation against closed valves

📌 Valve Status

• ALL FOUR VALVES ARE CLOSED (second closure event)

Pressure & Volume Changes

📌 Ventricular Volume (Vv)

• CONSTANT (no change)

📌 Ventricular Pressure (Pv)

• DECREASES significantly (due to ventricular relaxation)

📌 Atrial Pressure (Pa)

• INCREASES gradually (Atrium filling, but AV valve remains closed)

Heart Sound

📌 Second Heart Sound (S2)

• Heard during this phase
• Caused by closure of Semilunar Valves (Aortic and Pulmonary)

🟣 C. Rapid Filling Phase (0.15 sec)

📌 Valve Status

• Atrial pressure exceeds ventricular pressure
• Forces AV Valves (Mitral and Tricuspid) to OPEN
• Semilunar Valves: closed

📌 Blood Movement

• Rapid inflow of blood into Ventricle
• Approximately 80% of total filling occurs here

Pressure & Volume Changes

📌 Ventricular Pressure (Pv) & Volume (Vv)

• Both INCREASE rapidly

📌 Aortic Pressure (Ao/Pao)

• DECREASES

Heart Sound

📌 Third Heart Sound (S3)

• Heard during this phase

📌 S3 Classification

• Can be physiological: thin individuals, athletes, children
• Can be pathological

🟠 Clinical Note - Pathological Causes:

• Thyrotoxicosis
• Anemia
• Heart Failure
• If S3 and S4 heard together = Gallop Rhythm

🟣 D. Reduced Filling Phase (0.20 sec)

📌 Blood Portion

• Completes final 20% of ventricular filling

📌 Pressure & Volume

• Ventricular volume continues to increase (slowly)
• Pressures remain low or decrease slightly

🖇 IX. Summary of Blood Pressure Values (Clinical Note)

ParameterValueNotes

Systolic BP (Systemic/Aorta)

120-130 mmHg

Diastolic BP (Systemic/Aorta)

80 mmHg

Right Ventricular Systolic Pressure

25-30 mmHg

(Exam Point)

Pulmonary Artery Systolic Pressure

25-30 mmHg

Pulmonary Artery Diastolic Pressure

10 mmHg

(Exam Point)

🖇 X. Pressure-Volume Loop Curve Analysis

📌 Purpose

• Illustrates relationship between ventricular pressure and volume during cardiac cycle

📌 Loop Sequence

• B → C → D → A → B

🟣 Phase-by-Phase Analysis

1. Phase B → C: Isometric Contraction Phase

📌 Valve Status

• Mitral Valve: closes
• Aortic Valve: closed

📌 Action

• Ventricle contracts against closed valves
• Pressure increases sharply

2. Phase C → D: Ejection Phase

📌 Valve Status

• Aortic Valve opens at C

📌 Action

• Blood ejected
• Volume decreases

📌 Stroke Volume (SV)

• Width (diameter) between B-C line and D-A line = Stroke Volume
• Stroke Volume = blood ejected in one beat

3. Phase D → A: Isometric Relaxation Phase

📌 Valve Status

• Aortic Valve closes at D

📌 Action

• Ventricle relaxes
• Pressure drops rapidly
• Volume constant

4. Phase A → B: Ventricular Filling Phase

📌 Valve Status

• Mitral Valve opens at A

📌 Action

• Ventricle fills
• Volume increases

🖇 XI. Jugular Venous Pulse (JVP)

📌 Assessment Method

• Assessed using device called Phlebography

📌 Pulsation Characteristics

• Small veins: non-pulsatile
• Internal and External Jugular Veins: PULSATILE (Exam Point)
• Reason: large veins near heart

🟣 JVP Waveform Components

📌 Structure

• Three positive waves: A, C, V
• Three negative descents: X, X', Y

🟣 JVP Wave/Descent Analysis Table

Wave/DescentPolarityCorresponding Cardiac EventMechanism

A Wave

Positive

Atrial Systole

Contraction around orifices of Great Veins prevents backflow into Vena Cava

X Descent

Negative

Atrial Relaxation

Pressure drop following Atrial contraction

C Wave

Positive

Isometric Contraction

Bulging of AV Valves into Atrium (due to rising Ventricular pressure)

X' Descent

Negative

Systolic Volume Drop

Displacement/repositioning of AV valve

V Wave

Positive

Venous Filling (Diastole)

Accumulation of venous blood in Atrium against closed AV valve

Y Descent

Negative

Rapid Filling

Opening of AV valve; blood empties rapidly from Atrium into Ventricle

🟣 Clinical Applications

🟠 Canon A Wave (Exam Point)

📌 Definition

• Large, strong A wave

📌 Cause

• Generated when Atrium and Ventricle contract simultaneously (out of sequence)

📌 Conditions

• Tricuspid Stenosis
• Pulmonary Stenosis
• Hypertension

🟣 ECG Correlation

📌 A-C Interval

• In JVP: A-C Interval
• Corresponds to: P-R interval on ECG
• Reflects: A-V Nodal conduction time

🟣 Heart Block Patterns (Clinical Note)

TypeJVP Pattern

First Degree Heart Block

A-C interval is prolonged

Second Degree Heart Block

Not every A wave followed by C wave (e.g., 2 A followed by 1 C), but pattern maintained

Third Degree Heart Block

No relationship exists between A wave and C wave