Does decreased cardiac amount mean accumulation of blood to tissues/cells?

I'm trying to understand cardiac output.
So, to my knowledge, decreased cardiac output = less blood being ejected by the heart/ventricles per minute, right?

What does that mean, specifically? Does that mean more blood is accumulated somewhere else? Like in the tissues/cells..lungs?

If blood is accumulated somewhere else...for example the kidneys ..does that cause nocturia? Because blood contains sodium (in the plasma) right? So if there is a lot of blood in the kidneys.. the kidneys are excreting a lot of sodium..pee? But where would filtration fit into this. If there is a lot of blood in the kidneys.. would the kidneys have a hard time filtering? Is this why a K+ test is needed? I'm not sure If I'm making sense.. I'm trying to relate the two