wrong again.
To do it from heart is off course must (I agree here) but you really cant offer 5 time Namaz by heart only, you have to do it physically too. Thats the FIRST step of being practicing.
I agree with you in general, only thing is doing from heart is a best thing (not a must for peoples like us at this moment), I do prays 5 time (mostly) but to be honest i really do not know if even one of my prayer is really from heart. My heart is beyond my control all i could do is putting a proper effort to meet my obligation towards Allah.
Hopefully my heart would slowly follow me, please dua.