Kommentar zu Schemot 7:14

כבד — This word should be translated in the Targum by יקיר (his heart is hard — an adjective) and not by אתיקר (his heart has become Hard — a verb, as is given in some editions of Onkelos) because it is an adjective, just as (Exodus 18:18) “the thing is too heavy (כָּבֵד) for thee”.

כבד, Pharaoh had hardened his heart, as I explained already. (the word is a verb, not an adjective, compare Exodus 1,8 on the word מלא). In intransitive words applying to the body of a person, such as vayishman, he waxed fat, (Deut. 32,9) or vayichbad, he remained heavy, (Exodus 9,7) and several similar examples, constructed by a future tense with the prefix ו, the ordinary past tense would be kaved, or shamen.

כבד לב פרעה, even though Pharaoh could not help but notice the qualitative difference between what the sorcerers had done and what Moses and Aaron had accomplished.

ויאמר ה׳ אל משה כבד לב פרעה, G'd said to Moses: "Pharaoh's heart is stubborn, etc." What did G'd tell Moses here that he did not already know? Perhaps Pharaoh had not refused the request to let the Israelites go in so many words, but had merely remained silent after watching Aaron's demonstration. G'd informed Moses that the meaning of this silence was that Pharaoh refused to release the Israelites and did not even think it necessary to say so.