Animated mechanism visualizers
Physiology, step by step
Interactive, annotated walkthroughs of core physiology - the cardiac cycle, alveolar gas exchange, nephron transport, and hemodynamics - that step you through each phase so the mechanism clicks rather than getting lost in a block of text.
The cardiac cycle (Wiggers in plain terms)
step 1 / 6
Atrial systole
The atria squeeze, topping up the relaxed ventricles with blood through the open atrioventricular valves. Most filling is passive, but this final 'kick' completes it.
Ventricles are full and stretched (high preload).