Human Heart and Cardiac Cycle
Chambers, valves, conducting system and the phases of a heartbeat. (Biology › Body Fluids and Circulation, NEET UG syllabus.)
What is Human Heart and Cardiac Cycle?
The phase of contraction of the heart chambers, during which blood is pumped out.
Key formula / rule: Cardiac Output (CO)
Key points
- Identify and label the four chambers and major valves of the human heart.
- Describe the pathway of blood flow through the heart.
- Explain the structure and function of the cardiac conducting system (SA node, AV node, Bundle of His, Purkinje fibers).
- Detail the sequence of events during one complete cardiac cycle, including atrial systole, ventricular systole, and joint diastole.
Common exam trap
Confusing the roles of SA node and AV node.
Definitions
- Term
Systole
- Meaning
The phase of contraction of the heart chambers, during which blood is pumped out.
- Term
Diastole
- Meaning
The phase of relaxation of the heart chambers, during which they fill with blood.
- Term
Cardiac Cycle
- Meaning
The sequence of events that occur from the beginning of one heartbeat to the beginning of the next.
- Term
SA Node (Sinoatrial Node)
- Meaning
A specialized mass of cardiac muscle fibers located in the right atrium that acts as the natural pacemaker of the heart.
- Term
Stroke Volume (SV)
- Meaning
The volume of blood pumped out by each ventricle per beat.
- Term
Cardiac Output (CO)
- Meaning
The volume of blood pumped out by each ventricle per minute.
Learning objectives
Identify and label the four chambers and major valves of the human heart.
Describe the pathway of blood flow through the heart.
Explain the structure and function of the cardiac conducting system (SA node, AV node, Bundle of His, Purkinje fibers).
Detail the sequence of events during one complete cardiac cycle, including atrial systole, ventricular systole, and joint diastole.
Relate heart sounds ('lub', 'dup') to specific valve closures.
Define and calculate cardiac output and stroke volume.
Interpret a basic ECG waveform in relation to the cardiac cycle.
Formulae
- Name
Cardiac Output (CO)
- Note
Where HR is Heart Rate (beats/min) and SV is Stroke Volume (mL/beat). Typically around 5 L/min for a healthy adult.
- Expression
CO = HR × SV
Prerequisites
Basic understanding of human anatomy and physiology.
Knowledge of blood vessels and types of blood circulation (pulmonary and systemic).
Familiarity with cell structure and basic tissue types.
Common mistakes
Confusing the roles of SA node and AV node.
Incorrectly identifying which valves close to produce 'lub' and 'dup' sounds.
Mixing up the sequence of events in the cardiac cycle (e.g., atrial systole before ventricular systole).
Forgetting the duration of each phase of the cardiac cycle.
Not understanding the difference between stroke volume and cardiac output.
Misidentifying the location of different valves.
Keywords
Heart
Cardiac Cycle
SA Node
AV Node
Systole
Diastole
Tricuspid Valve
Bicuspid Valve
Semilunar Valves
Cardiac Output
Stroke Volume
ECG
Pacemaker
Practice preview
Which of the following correctly represents the sequence of events during a single cardiac cycle, starting from atrial systole?…
medium
The tricuspid valve is located between which two chambers of the human heart?…
easy
Damage to the Atrioventricular (AV) node would most directly affect which of the following?…
medium