When did he call?
Radak: When he was afflicted.
Why does it say "b'Chol Lev {Aneni}"?
Radak: I know that no one answers and saves other than You.
Malbim: Because I guard Your Chukim, this obligates You to hear my Tefilah. This is the Segulah of the Chukim!
What is the connection of "Chukecha Etzorah" to what came before?
Radak: Answer me, so I will not die in the hands of my enemies. I request life only in order to guard Your Chukim!
Malbim: It says "Asher Yishme'un Es ha'Chukim ha'Eleh v'Amru Rak Chachmah v'Navon ha'Goy ha'Gadol ha'Zeh; ... Elokim Kerovim Elav... b'Chol Kar'enu Elav" (Devarim 4:6-7). I.e. they will see that via the Chukim, Hashem hears Yisrael's Tefilah and answers them when they call to Him. I.e. there is great Chachmah in the Chukim. Chukim of the Torah correspond to Chukim of the world. Via guarding the former, He guards for them also the latter - "Im b'Chukosai Telechu; v'Nasati Gishmeichem b'Itam" (Vayikra 26:3-4).
