It depends on the particular ecosystem and why and how it was destroyed. It can take just 2 years or over 100 years depending on the different factors. Sometimes ecosystems never recover.
What do you mean by your question
Having traveled through the arteries and capillaries, the blood have already lost considerable amount of pressure when it is to travel through the veins. The veins are composed of one-way valves as when the veins are squeezed, it pushes the blood to the valves.
