From the diagram you can work out the factors on the arterial side which govern mean arterial pressure. If the veins are stiffer, when I put a certain volume in, the pressure will rise more, because the compliance is less. By changing the rate of depth of respiration, I can alter venous return. If I move around, I can actually increase venous return. This has to be regulated.
Venous return leads to filling of the heart.
The cardiopulmonary baroreceptors in the heart sense the change in volume and this causes receptor activation by stretch. The cardiopulmonary baroreceptors interact with the arterial baroreceptors and play an important, but not yet completely defined, role in cardiovascular pressure regulation. They are stimulated when they are distended. An increased stretch of the mechanoreceptors initiates increased traffic in the afferent nerves connecting them with the solitary tract nucleus. As a consequence the vagal center and the inhibitory neurons of the vasomotor center are activated.