R. Yonah: They are people with bad Midos. Midos are attributed to the heart - "v'Shome'a Tochachas Koneh Lev", "Liknos Chachmah v'Lev Ayin" (15:32, 17:16). Hashem despises them, like it says "To'avas Hashem Kol Gevah Lev" (16:5). Therefore, one should arouse himself to make all efforts to remove bad Midos, lest he be To'avas Hashem, and acquire good Midos, to be pleasing to Him.

Malbim: This is the opposite of Chacham Lev (refer to 11:20:2:2). He argues with the laws of Chachmah, and conducts oppositely.

R. Yonah: They are people born with pure Midos ¹ , or they changed their Midos according to Sechel, like I explained above (3:5). This pleases Hashem - "ha'Adam Yir'eh l'Einayim va'Shem Yir'eh l'Levav" (Shmuel I, 16:7); Hashem desires the heart (Sanhedrin 106b). "Lev Tahor Bara Li Elokim" (Tehilim 51:12) - a heart pure from (without) lusts. Hashem desires Maskilim (those who grow wise) - "Retzon Melech l'Eved Maskil" (14:35).

Malbim: The heart is the power that rules in man and conducts all his powers according to the laws of Chachmah and Tzedek. One who does so constantly is Chacham Lev; then, he is Tamim Derech. His actions are always pure. He never falters to veer from the path via desires and the Yetzarim of the heart, for the heart rules with Yir'as Hashem. Hashem desires him.

Malbim: No. Some are in the middle - not Ikesh Lev to argue with the laws of Chachmah, and not Tamim Derech. Sometimes he veers from the path if the Ru'ach of the Yetzer ha'Ra comes upon him. He is not l'Ratzon, and not To'evah. He is amidst the war [against the Yetzer] - to defeat it or be defeated.