Fig. 5.

Velocity flow field of some embryonic hearts at HH25. Other samples are shown in supplementary Fig. 3. a Contraction of the ventricle during systole pumps blood out into the outflow tract. b Expansion of the ventricle draws blood from the atria through atrioventricular junction with aid of atria contraction. c Atrial contraction expired, leaving the ventricle to draw its inflow directly from the sinus venosus. “Through-flow” or flow moving from the veins towards the ventricle without atrial pumping aid occurs. Yellow arrow indicates atrial inlet. d Temporal peak of the volume-averaged velocity in the ventricle during diastole. * p < 0.05