[R] par("usr") when used in heatmap()

[array chip]

Hi, is there anyway I can retrieve the user coordinates for the region of the 
heatmap (only the heatmap, not include dendrogram, x- & y- axis annotation). I 
found that par("usr") didn't give the user coordinates that I want. I want those 
user coordinates to add some additional information to the outside of the 
heatmap region (some text, some lines, etc). 


par("usr") works perfectly with image().?

Thanks