'The heart moves; the world moves.'
- Pounding Airs
Heart is one of the Principles of the invisible arts, named after the Heart Relentless. It is the aspect of life, ceaseless motion, protection, and preservation.
'There are common sentiments in every thunderclap. - Let us acknowledge them.''
- A Thunderous Secret
The Principle of Heart is most commonly represented through music (particularly drums) and dance, expressions of vitality and motion. Storms, thunder, and the sea are also common symbols, as the Heart Hours contend to stir and quell these forces. The aspect is commonly used to heal and invigorate the body and can also ward against a variety of perils both natural and supernatural.
Despite Heart’s focus on life and protection, the Principle can be as dangerous as any other. Common themes of its rituals include flaying and other forms of brutal sacrifice, and its servants often express manic, obsessive tendencies. Those who take up Heart’s vigil do not cease, and interruptions to their work are rarely excused. 
'In the vision the trunks of the pines are lit by the fire but the shadows of the dancers come and go in a zoetrope flicker. With each stroke of the drum I am freed from another slip of skin, but it is not St Agnes who holds the knife, and at last I can bear no more and all the pent screams burst from me.'
- A Vision of the Pines
In the Dancer DLC of Cultist Simulator, the player can choose to pursue the dances of the New Form, the Heart variant of the Change Ascension. This involves venturing out in various animal shapes to learn seven lessons of Change from the Hours, culminating in a final performance and sacrifice with the Flaying Key to join the dance of the Thunderskin in the Mansus. It is unclear whether this is the “standard” method of ascension for Heart-Long, or even if the player becomes a true Long from this process, though they do pass the Tricuspid Gate.
'Even in the snow, in the silence, in the white without colours, life will never quite cease.'
- Subvert the Ragged Lore
In Cultist Simulator, Heart subverts Winter, and the two principles are often interpreted as opposites. Winter is the aspect of death and endings while Heart embodies life and eternity. Though Winter may fall upon the earth, Spring inevitably returns, as does life in the wake of death.
Heart itself is subverted by Grail, for the Heart is Blood’s Drum, as life succumbs to hunger and desire. The Thunderskin itself was once a Name of the Red Grail, who orchestrated his sacrifice and ascension in part to challenge the Twins for dominion over the aspect. The Twins also served the Red Grail before growing too powerful.
'The Grail ripped the Thunderskin from flesh. The Sister-and-Witch was born from two wombs. The Velvet woke when the Wood-roots tasted blood. The Heart is Blood's Drum, and here is its secret doctrine....'
- The Unceasing Mysteries
'That which does not cease, is not ceased.'
- Read 'The Ceaseless Tantra'
1. Dorothy, a Tarantellist 2. The Sailor's Surety 3. Heal a Wound with Vitality 4. We call upon the Ring-Yew, who is renewed 5. Study "Apollo and Marsyas" 6. Duende Midnight 7. The New Form 8. The Kingskin Gate 9. LIFE, UNENDING 10. The Life Beneath 11. Unceasing Mysteries 12. The Life Beneath 13. Read 'Those Who Do Not Sleep' 14. Summon a creature of the Thunderskin 15. Read 'The Flayed Tantra' 16. Search for Something Unseen 17. At the Fane of Owls 18. Count Jannings 19. Jannings, the Vivisectionist