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Quizzes > Health & Medicine

Cardiac Cycle Quiz: ECG Events and Valve Actions

Quick, free quiz on ECG phases and valve timing. Instant results.

Editorial: Review CompletedCreated By: Daydreamermagicgirl OliveriUpdated Aug 27, 2025
Difficulty: Moderate
Grade: Grade 10
Study OutcomesCheat Sheet
Colorful paper art promoting Cardiac Cycle Challenge quiz for advanced students

This cardiac cycle quiz helps you check ECG events and valve actions across systole and diastole. Answer 20 quick questions to build recall and get instant feedback on what to study next. For more practice, review rhythms with our dysrhythmia quiz, explore volume changes in the stroke volume quiz, or refresh structures with the parts of the heart quiz.

What is the primary pacemaker of the heart?
Atrioventricular (AV) node
Sinoatrial (SA) node
Purkinje fibers
Bundle of His
The sinoatrial node initiates the heartbeat and sets the rhythm for the heart. It is considered the primary pacemaker because it generates the electrical impulses that trigger cardiac contractions.
Which of the following best describes the systole phase?
The phase of valve closure
The phase where the heart relaxes and fills with blood
The phase of electrical depolarization
The phase where the heart contracts to pump blood out
Systole is the phase during which the heart contracts, forcing blood out of the chambers. This contraction is essential for circulating blood throughout the body.
What component of the heart prevents backflow of blood from the ventricles to the atria?
Chordae tendineae
Papillary muscles
Atrioventricular (AV) valves
Semilunar valves
Atrioventricular valves, including the mitral and tricuspid valves, close during ventricular contraction to prevent backflow into the atria. Their proper functioning is vital for unidirectional blood flow.
During the cardiac cycle, what is the phase when the ventricles fill with blood?
Systole
Atrial systole
Isovolumetric contraction
Diastole
Diastole is the phase during which the heart muscles relax, allowing the ventricles to fill with blood. Proper ventricular filling is essential for an effective subsequent contraction.
What event causes the 'lub' sound heard during the cardiac cycle?
Atrial contraction
Opening of the semilunar valves
Ventricular contraction
Closure of the atrioventricular valves
The 'lub' sound, or the first heart sound, is produced by the closure of the atrioventricular valves at the onset of ventricular systole. This sound indicates that the ventricles are about to contract.
Which phase of the ventricular cycle occurs immediately after the closure of the atrioventricular valves?
Ejection phase
Isovolumetric relaxation
Isovolumetric contraction
Diastolic filling
Immediately after the atrioventricular valves close, the ventricles begin contracting without a change in volume, which marks the isovolumetric contraction phase. This phase builds up the pressure needed to open the semilunar valves for blood ejection.
During the isovolumetric contraction phase, what happens to the volume of blood in the ventricles?
It decreases
It fluctuates
It increases
It remains constant
With all valves closed during isovolumetric contraction, the blood volume in the ventricles stays the same even as internal pressure rises. This phase is critical for developing the force required for the ejection phase.
Which of the following describes the isovolumetric relaxation phase?
Ventricular pressure decreases without a change in volume
Ventricular walls continue to contract
Ventricular volume increases suddenly
Atrial contraction aids in filling
During isovolumetric relaxation, ventricular pressure falls while the volume remains constant because all valves are still closed. This decline in pressure is necessary to prepare the ventricles for the next phase of filling.
Which heart valve opens to allow blood to exit the left ventricle into the aorta?
Tricuspid valve
Aortic valve
Pulmonary valve
Mitral valve
The aortic valve opens during the ejection phase to let blood flow from the left ventricle into the aorta. Its proper timing ensures efficient systemic circulation.
What electrical event corresponds to the QRS complex on an ECG?
Ventricular depolarization
Atrial repolarization
Ventricular repolarization
Atrial depolarization
The QRS complex represents the rapid depolarization of the ventricles, which triggers ventricular contraction. It is a key component of the ECG that reflects electrical activity during the cardiac cycle.
How does the atrial systole contribute to the cardiac cycle?
It is responsible for closing the semilunar valves
It significantly reduces ventricular pressure
It provides an extra push that increases ventricular filling
It initiates ventricular contraction
Atrial systole contracts the atria, giving an extra push that tops off the ventricles with additional blood. This enhanced filling improves the overall stroke volume during ventricular contraction.
Which structure delays the electrical impulse allowing the ventricles time to fill?
Bundle of His
Atrioventricular (AV) node
Sinoatrial (SA) node
Purkinje fibers
The AV node slows the transmission of the electrical impulse from the atria to the ventricles. This delay ensures that the ventricles have sufficient time to fill before they contract.
What is the main purpose of the isovolumetric contraction phase?
To allow the ventricles to relax and fill
To ensure closure of the semilunar valves
To decrease blood volume in the ventricles
To build up pressure within the ventricles before blood ejection
During isovolumetric contraction, the ventricles contract without changing volume, causing a buildup of pressure. This increase in pressure is essential to overcome arterial pressure when the semilunar valves open for ejection.
In the cardiac cycle, during which phase are the semilunar valves open?
Isovolumetric contraction
Isovolumetric relaxation
Ejection phase
Diastole
During the ejection phase, ventricular pressure exceeds arterial pressure, resulting in the opening of the semilunar valves. This allows blood to be propelled into the aorta and pulmonary artery.
Which of the following best explains the function of the Purkinje fibers?
They rapidly transmit the electrical impulse through the ventricular muscle
They initiate the heartbeat
They control the opening of the atrioventricular valves
They delay impulse conduction between the atria and ventricles
Purkinje fibers are specialized cells that quickly distribute the electrical impulse throughout the ventricles. This rapid transmission ensures a synchronized and efficient contraction of the ventricular muscle.
During diastole, what ensures that the ventricles properly fill with blood?
Rapid closure of the semilunar valves
High ventricular pressure
Relaxation and low pressure in the ventricles
Contraction of the ventricular walls
During diastole, the relaxation of ventricular muscle leads to a drop in chamber pressure. This low-pressure environment facilitates the passive flow of blood from the atria into the ventricles.
Which phase directly precedes the isovolumetric relaxation phase in the cardiac cycle?
Diastolic filling
Isovolumetric contraction
Atrial systole
Ejection phase
The ejection phase, during which blood is expelled from the ventricles, immediately precedes the isovolumetric relaxation phase. Once the blood has been ejected, the ventricles begin to relax without any change in volume.
Which event marks the beginning of ventricular repolarization?
The beginning of the T wave
The onset of the P wave
The end of the QRS complex
The PR interval
The T wave represents the start of ventricular repolarization, where the ventricles return to their resting state. This follows the depolarization phase that is captured by the QRS complex on an ECG.
What physiological change occurs during the ejection phase?
Blood is forced out of the ventricles into the arteries
The atrioventricular valves open
The ventricles fill with blood
Ventricular pressure drops significantly
In the ejection phase, the high intraventricular pressure drives blood out of the ventricles and into the systemic and pulmonary circulations. This phase is essential for the effective propulsion of blood to the body and lungs.
How does the structure of the cardiac muscle contribute to efficient contractions during the cardiac cycle?
It has abundant gap junctions for coordinated contraction
It relies solely on external neural stimulation
It lacks intercalated discs
It has long refractory periods that limit contractions
Cardiac muscle cells are interconnected by intercalated discs that contain gap junctions, allowing rapid electrical coupling between cells. This arrangement ensures that the contraction of the heart muscle is synchronized for efficient blood pumping.
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Study Outcomes

  1. Understand the sequence and phases of the cardiac cycle.
  2. Analyze the relationship between electrical activity and mechanical contractions in the heart.
  3. Apply cardiovascular physiology concepts to clinical scenarios.
  4. Evaluate the impact of hemodynamic changes during different stages of the cycle.
  5. Interpret data from interactive cardiac physiology questions to assess learning progress.

Cardiac Cycle Review Cheat Sheet

  1. Phases of the Cardiac Cycle - Picture your heart in three acts: atrial systole tops up the ventricles, ventricular systole pumps blood out, and diastole lets the chambers relax and refill. Understanding these steps is like learning the choreography of blood flow.
  2. Heart Sounds: "Lub" and "Dub" - Every heartbeat makes a duet of sounds: "lub" (S1) when the atrioventricular valves close, and "dub" (S2) when the semilunar valves seal. Learning to match these clicks to valve action turns auscultation into a superpower.
  3. Wiggers Diagram - This trusty chart maps pressures, volumes, and valve events across the cycle, making complex timing crystal clear. Think of it as a roadmap for every heartbeat twist and turn.
  4. Cardiac Volumes: EDV & ESV - End-diastolic volume (EDV) is the fill-up before the big squeeze, and end-systolic volume (ESV) is what's left afterward. Subtracting ESV from EDV gives stroke volume, your per-beat output.
  5. Cardiac Output - This measures how much blood your heart pumps per minute: CO = Stroke Volume × Heart Rate. It's your heart's performance score, showing how well it meets the body's demands.
  6. Ejection Fraction - Ejection fraction tells the percentage of blood ejected each beat with EF = (SV/EDV)×100%. A healthy heart typically knocks out around 55 - 70% per contraction.
  7. Valve Roles - Atrioventricular valves (tricuspid and mitral) steer blood from atria to ventricles, while semilunar valves (aortic and pulmonary) guard the exits. Together, they prevent backflow and keep circulation one-way.
  8. Phase Durations - In a 0.8-second cycle, atrial systole lasts ~0.1s, ventricular systole ~0.3s, and diastole ~0.4s. Knowing these timings helps predict how heart rate changes impact each phase.
  9. ECG and the Cardiac Cycle - The P wave marks atrial depolarization, the QRS complex shows ventricular depolarization (and systole), and the T wave aligns with repolarization (diastole). Linking ECG peaks to mechanical events ties electrical signals to actual heart action.
  10. Heart Rate Effects - As your HR climbs, each cardiac cycle compresses in time, especially shortening diastole. Understanding this explains why extreme exercise or tachycardia can impact filling and output.
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