Or (by meditation on) the heart that has given up all attachment to sense-objects.
In plain words: Or calm the mind by meditating on the heart of someone who has let go of craving for worldly things. The teacher says to think of a saint you respect.
Take some holy person, some great person whom you revere, some saint whom you know to be perfectly non-attached, and think of his heart. That heart has become non-attached, and meditate on that heart; it will calm the mind. If you cannot do that, there is the next way:
Namaste.
A calm guide to life, the mind and the old teachings.