a song in (one's) heart
An intense, euphoric feeling of happiness and contentment. Even though he left school when he was 16, my dad still found a career that he could do with a smile on his face and a song in his heart. There's nothing like driving along a sunny coast in the sunshine to put a song in your heart.
a song in your heart
a feeling of great or euphoric happiness. The expression originated in the title of a song, ‘With a song in my heart’ ( 1929 ), by Lorenz Hart .