Note:This video sequence demonstrates the heart's contraction-relaxation cycle. The portion of the cardiac cycle marked by relaxation of the ventricles is called diastole. The portion of the cardiac cycle marked by contraction of the ventricles is called systole.
4. 1st pharyngeal arch (mandibular process)
5. right edge of mouth (stomodeum)
6. umbilical cord in the background
7. abdominal wall
9. heart chambers (outlined in yellow)
|All ages referenced to fertilization, not last menstrual period.|