Why does it say "Ta'avas Libo Nasata Lo"?
Malbim: Salvation via people is not like a person's heart desired, for he is ashamed to request everything in his heart. However, You gave everything in his heart.
Did Hashem already give to him "Ta'avas Libo"?
Radak: No. Nasata is like Titen (You will give). Nevu'ah often uses past tense in place of future, like I wrote above (3:5. Nevu'ah for the future exists, as if [already] came - Radak Yirmeyah 46:23.) The same applies to "Areses Sefasav Bal Manata."
What is "Areses Sefasav"?
Rashi: It is an expression of speech. There is nothing like this in Tanach. Menachem says that it is like "k'Rishyon Koresh Melech Paras" (Ezra 3:7). Both are expressions of utterances of the lips.
Why does it say "Areses Sefasav Bal Manata"?
Malbim: What he says is done automatically, for nature heeds him. It is as if You need not give to him, just not to stop nature from giving to him.