Slicing an unstructured mesh

I am displaying a slice of some results (flow simulations from PYFR, if this makes a difference) in an unstructured mesh, and it is rather fuzzy looking. I was thinking this might have to do with the mesh being unstructured in the direction I am slicing. I mean that the slice cuts through different cells at different points. Is there some recomended procedure for slicing an unstructured grid? should I use some filters first?

Can you provide a screenshot of the issue ?