Thanks guys !
The -v flag shows the in/out interface for each rule. All I need to do is filter the output with grep to show only the rules for the interface I am interest at.
I read the iptables man pages several times, and my mind was stucked on looking for a iptables flag/option to show only the interface I want. I never realized I can filter it later.
anyway, thanks for the answers. They really make me to see the obvious.
I guess I am not thinking right since Brazil is out of World Cup