Blood flow is the flow of blood in the cardiovascular system. It is described by the Ohm's law and approximately by Hagen-Poiseuille's law (because it is accurate only for Newtonian fluids, while blood is not Newtonian and its flow can be described as laminar only in smaller vessels, elsewhere it is turbulent). The upper equation is Ohm's law, you get the Hagen-Poiseuille's law if you insert the lower in it (it is also written in its own article, see link above):

where:

In the last equation it is important to note that blood flow changes with the fourth power with change of radius. This is important in angioplasty, as it enables the increase of blood flow with balloon catheter to the deprived organ significantly with only a small increase in radius of a vessel.