As the head turns, blood cells are visible in the heart. A network of vessels that feed into the embryo's circulatory system is visible. The outflow tract of the heart is seen with the emptying of blood into the arterial circulation. The whole embryo is again seen in the context of its extra-embryonic circulation. Several days later, the embryo is seen over the yolk with a well-developed circulatory system and sequential atrial and ventricular contractions.
Blood streams in from the network over the yolk and is pumped to the embryo by the heart.