Is there a negative net flow of blood in human arteries at any point of the cardiac cycle? I realise that blood flow can be turbulent, e.g. in the aorta or around stenotic arteries, but then the average is still flowing away from the heart.
The question was provoked by this graph, which admittedly I haven't seen in its context:
A similar graph showed negative velocities in the aorta and innominate artery of humans.
Simple answer, yes.
It really is a matter of how technical you wish to be. By defintion, all arterial flow conveys blood away from the heart. The largest arteries exhibit the Windkessel effect which allows for the compression-based effects that bobthejoe inferred. Explicity, as blood is pumped out of the left ventricle, it stretches te aorta, and this tension in turn causes compression on the artery and pushes blood forward. On the flip side, venous vessels (except the pulmonary vein) return blood to the heart, but here you are likely to encounter local areas of reverse flow. This is counteracted to a degree by one-way valves present in the large veins to keep the net movement of blood in the body always toward the heart.
Quick answer, no.
Imagine a balloon; as you compress the balloon, there will be a lot of air that leaves it. But as you let it relax, the balloon pulls in surrounding air even as you fill it from another side. When the aortic and tricuspid valves are closed, there is blood flow forward but due to conservation of mass, the blood goes back to fill in the empty region.
