In Figure 6-39, the heart appears to the left of the eyespot. It extends along the anterior—ventral surface of the embryo from the anterior vena cava to past the eye and along the ventral surface of the embryo. When the movie is activated, the beat of the heart is from anterior to posterior. The initiation of the heart’s ventricular beat can be seen originating just left of the eyespot. The ventricles’ strong beat appears to draw blood into to differentiating atrium (darker color). The heart extends along the anterior—ventral surface of the embryonic body and the strong beating of the ventricle can be seen just left of the eye, which produces blood flow from anterior blood vessels into the posterior differentiating atrium (see Figure 6-39).