Wait, why didn't Tsunade hear Madara's heart beat when he was hiding beneath her in the tree and stabbed her?
Gotcha.
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Let's say she can hear heart beats when concentrating, but then, we have no proper information on it.
- Which distance does it reach?
- Does she need to concentrate properly, what would disable her for fight? Since Shee, a sensor, said he wouldn't be able to fight properly while tracking someone.
So all this argument is invalid, since no proper information is given, we don't know how it would work during a real battle. Anything said here is fan fiction based on no facts.
/Discussion.
