Mahmā is a jussive conditional noun meaning “whatever.” Taʾmurī is a feminine singular imperfect in the conditional clause; its jussive form drops the nūn of the five verbal forms. Al-qalba is its direct object.
Yafʿal is the response to the condition and grammatically belongs to the jussive construction. Its final audible kasrah is to be read in the setting of poetic pronunciation and rhyme. The sense is “whatever you command, the heart performs”.
ElementFunction
MahmāConditional noun
TaʾmurīConditional verb; feminine addressee
Al-qalbaDirect object
YafʿalApodosis: response to the condition