The cockle shell became the badge of Santiago pilgrims — and "warming the cockles of your heart" may refer to the heart-shaped shells or the Latin name for heart chambers.
A small, edible saltwater bivalve mollusk with a ribbed, heart-shaped shell. The expression "warm the cockles of your heart" refers to causing a feeling of warmth and happiness.
From Old French coquille (shell), from Latin conchylium (shellfish, mussel), from Greek konchylion (little shell), diminutive of konchē (mussel, shell). Possibly influenced by Middle English cokel (the grain weed cockle) Key roots: conchylium (Latin: "shellfish, mussel"), konchē (Greek: "mussel, shell").
The phrase "warm the cockles of your heart" may refer to the heart-shaped shells of cockles, but another theory connects "cockles" to Latin cochleae cordis — the chambers (literally 'snail shells') of the heart, which early anatomists noted for their spiral shape. The cockle shell is the emblem of the Camino de Santiago pilgrimage — medieval pilgrims to Santiago de Compostela wore cockle shells as proof of completing the journey. Molly Malone, Dublin's legendary fishmonger of song