manipulating arrows
 

Does anyone know how to manipulate the size and direction of an arrow using a
macro? I have a simple macro, that imports data (numbers) from a .txt file
and with that data creates a simple drawing (map of Europe, where countries
are represented with groups of cells). In this drawing are arrows, pointing
from one country to another, but their size and direction is fixed. How can I
make them change their size (depending on the value of the imported number)
and the direction they are pointing (depending on if the imported number is
positive or negative)?
Thanks, Jan