This deep dive covers The Cardiac Cycle: How Your Heart Beats within The Heart and Circulation for GCSE Biology. Heart structure, cardiac cycle, blood vessels, double circulation, heart rate control, and cardiovascular health It is section 3 of 15 in this topic. Use this deep dive to connect the idea to the wider topic before moving on to questions and flashcards.
The Cardiac Cycle: How Your Heart Beats
1. Atrial Systole (0.1 seconds)
- Both atria contract simultaneously
- AV valves (tricuspid and bicuspid) are open
- Blood pushed from atria to ventricles
- Ventricles fill completely (end-diastolic volume)
- Semi-lunar valves (pulmonary and aortic) remain closed
2. Ventricular Systole (0.3 seconds)
- Both ventricles contract with massive force
- AV valves snap shut → first heart sound "LUB"
- Pressure builds in ventricles
- Semi-lunar valves forced open
- Blood ejected into aorta and pulmonary artery
- This creates your pulse and blood pressure
3. Complete Diastole (0.4 seconds)
- All chambers relax
- Semi-lunar valves snap shut → second heart sound "DUB"
- AV valves open as pressure drops
- Blood flows passively from atria to ventricles
- Coronary arteries fill with blood (heart muscle fed)
- Cycle ready to repeat
Cardiac Output Calculation
Cardiac Output = Heart Rate × Stroke Volume
Example: Resting adult
- Heart Rate = 70 beats per minute
- Stroke Volume = 70 ml per beat
- Cardiac Output = 70 × 70 = 4,900 ml/min ≈ 5 litres/min
During Exercise:
- Heart Rate can increase to 180+ bpm
- Stroke Volume can increase to 120+ ml
- Cardiac Output can reach 20+ litres/min
Practice questions for The Heart and Circulation
How many chambers does the human heart have?
Explain how the structure of an artery is related to its function.
Quick recall flashcards
What is systole?
When the heart contracts and pumps blood out of the ventricles
What is diastole?
When the heart relaxes and the chambers fill with blood