From a skeptical translation point of view, I want to know if the word heart means the same thing today as it did then.

I’m sure that part is mostly accurate, but I think it’s talking about other people’s hearts, rather than one’s own.

In context, it’s trying to make a point about how one should trust god above men, because there’s no way for one to know how another person truly feels (but in theory god can).

You’d have to ask a theologian for an actual answer.