In tonglen practice, when we see or feel suffering, we breathe in with the notion of completely feeling it, accepting it, and owning it. Then we breathe out, radiating compassion, lovingkindness, freshness - anything that encourages relaxation and openness. So you're training in softening, rather than tightening, your heart. In this practice, it's not uncommon to find yourself blocked, because you come face to face with your own fear, resistance, or whatever your personal "stuckness" happens to be at that moment.
Pema ChodronAt some point, we realize that what we do for ourselves benefits others, and what we do for others benefits us.
Pema ChodronWhat's encouraging about meditation is that, even if we shut down, we can no longer shut down in ignorance. We see very clearly that we're closing off. That in itself begins to illuminate the darkness of ignorance.
Pema Chodron