Circulatory System: The Heart, Its Cycle, Vessels and Blood Groups

In the paper

The circulatory system is the most-asked chapter of Human Biology, usually two or three of the fifteen questions. MEC lists six points — "Heart; Cardiac cycle and cardiac output; Heartbeat; Arterial and venous system; Blood groups and blood pressure; Concept of cardiovascular disorders" — the last new in 2026. The usual angles:

• Recall: a cardiac-cycle timing, which valve makes which sound, the ECG wave for atrial depolarisation.
• Understanding: why the AV node delays the impulse, why the left ventricle is thicker, why the second Rh-positive baby is at risk.
• Application: compute cardiac output, choose a donor for a recipient, interpret 150/95, explain chest pain on climbing stairs.