Why an exploding heart?

IDP has a new t-shirt. Compared to the last -- "this body will be a corpse" -- which aroused strong reactions, this one seems pretty benign. It has a heart with a thunderbolt breaking it open, surrounded by a jagged line that usually goes around explosive remarks in comics -- BAM! POW! -- and it says "metta," the Pali word for loving-kindness.

I'm confused, though. My understanding of metta is that it is gentle, inviting ourselves and then others into the loving energy of our basic goodness. It's patient and kind. It's not explosive. Karuna, or compassion, is explosive -- it breaks your heart open and spreads your love out so that it encompasses all living beings.

So why an exploding heart with metta?

Please, someone with decision-making powers at IDP, explain.

According to accesstoinsight.org: "The Pali word metta is a multi-significant term meaning loving-kindness, friendliness, goodwill, benevolence, fellowship, amity, concord, inoffensiveness and non-violence. The Pali commentators define metta as the strong wish for the welfare and happiness of others (parahita-parasukha-kamana). Essentially metta is an altruistic attitude of love and friendliness as distinguished from mere amiability based on self-interest. Through metta one refuses to be offensive and renounces bitterness, resentment and animosity of every kind, developing instead a mind of friendliness, accommodativeness and benevolence which seeks the well-being and happiness of others. True metta is devoid of self-interest. It evokes within a warm-hearted feeling of fellowship, sympathy and love, which grows boundless with practice and overcomes all social, religious, racial, political and economic barriers. Metta is indeed a universal, unselfish and all-embracing love."

Metta practice usually starts with extending loving-kindness to yourself. (Although I learned it from IDP founder Ethan Nichtern's father, David, a senior teacher in the Shambhala lineage, by starting with a being you love dearly, like a child, grandparent, or dog, raising the sense of unconditional love, then releasing that person and bringing yourself into that same atmosphere. I cried the first time I did it.).

In her book "Loving Kindness: The Revolutionary Art of Happiness," IDP lineage mentor Sharon Salzberg  quotes the Buddha: "You can search throughout the entire universe for someone who is more deserving of your love and affection than you are yourself, and that person is not to be found anywhere. You yourself, as much as anybody in the entire universe, deserve your love and affection."

Then you extend it to others -- a person you love, a neutral person, a difficult person, the people nearby, all beings. It's a deep practice that truly does change the way you look at the world. It's also my main practice at the moment after a difficult holiday season where I feel into habitual patterns of thinking that had me trying to be the perfect wife, mother, daughter, sister, friend to everyone but myself, thinking everyone else was more deserving of my love and affection.

Buddha says: Bring it back, girlfriend.

The metta sutta says:
Even as a mother protects with her life
Her child, her only child,
So with a boundless heart
Should one cherish all living beings:
Radiating kindness over the entire world
Spreading upwards to the skies,
And downwards to the depths.

There's also a traditional instruction from the Buddha that in metta meditation you should regard yourself as a mother cow looks at her calf.

so enlighten me, decision makers -- why the exploding heart for metta?