D4  The Heart

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Essential Idea:

Internal and external factors

influence heart function


  • Structure of cardiac muscle cells allows propagation of stimuli through the heart wall
  • Signals from the sinoatrial node that cause contraction cannot pass directly from atria to ventricles
  • There is a delay between the arrival and passing on of a stimulus at the atrioventricular node
  • This delay allows time for atrial systole before the atrioventricular valves close
  • Conducting fibres ensure coordinated contraction of the entire ventricle wall
  • Normal heart sounds are caused by the atrioventricular valves and semilunar valves closing causing changes in blood flow


  • Use of artificial pacemakers to regulate the heart rate
  • Use of defibrillation to treat life-threatening cardiac conditions
  • Causes and consequences of hypertension and thrombosis


  • Measurement and interpretation of the heart rate under different conditions
  • Interpretation of systolic and diastolic blood pressure measurements
  • Mapping of the cardiac cycle to a normal ECG trace
  • Analysis of epidemiological data relating to the incidence of coronary heart disease