Coordinating the heartbeat
Coordinating the heartbeat

The heart has two atria and two ventricles. For efficient pumping, the atria contract first to top up the ventricles, then the ventricles contract from the apex upwards; relaxation is called diastole.
Step-by-step lessons on Edexcel A A Level Biology Cardiac control, ECGs and exercise physiology. Each one builds up to exam-style questions. Build a strong foundation in cell biology and biochemistry early on, since later topics on genetics, ecology and physiology all draw on these core concepts.