warm the cockles of (one's) heart
To cause one to feel happy. The "cockles of one's heart" are the deepest part of oneself. Thank you so much—your kind words really warmed the cockles of my heart.
warm the ˈcockles (of somebody’s ˈheart)
(British English) make somebody feel happy or sympathetic: Ah! It warms the cockles of my heart to see the children so happy.