In what ways does Puck follow his heart in A Midsummer Night's Dream?

I rather think how you answer this question depends on
your own personal ideas about Puck and the kind of role he plays in the play. This is of
course where subtext comes in: how we interpret the lines that we are given of the play.
We must recognise that directors who have staged the play have produced very different
kind of Pucks over the years.

My own feeling about Puck has
always been that he is a force of chaos in the play who delights in making things more
complicated than they actually are. If I were a director, I would show this by having
Puck deliberately confuse the Athenian lovers to create a more complicated situation for
his own amusement. We can see his delight in causing chaos especially when he transforms
Bottom and then chases away th other players in Act III scene
1:

I'll
follow you, I'll lead you about a round,

Through bog,
through bush, through brake, through brier.

Sometimes a
horse I'll be, sometimes a hound,

A hog, a headless bear,
sometimes a fire...

We can
see the intense enjoyment that Puck takes in scaring the players and frightening them
away.

In addition, note how Puck is pleased by the prospect
of both Lysander and Demetrius being in love with Helena after Demetrius has had his
eyes annointed in Act III scene 2:

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Then will two at once woo
one;

That must needs be sport
alone.

And those things do best please
me

That befall
preposterously.

Puck loves
things that "befall preposterously," as they provide him with intense enjoyment. All of
this points towards the way in which Puck most definitely follows his heart in this
hilarious comedy. He is a force of chaos, and he acts to be true to
this.