"Secret of My Heart" is a song by Japanese singer songwriter Mai Kuraki, taken from her debut album Delicious Way (2000). It was released on April 26, 2000, and peaked at number two on the Oricon Weekly Singles Chart.
"Secret of My Heart" debuted at number two on the Oricon Weekly Singles Chart with 410,550 physical copies sold. The song charted on the chart for 16 weeks and has sold over 968,980 physical copies. "Secret of My Heart" became the singer's second best-selling song behind "Love, Day After Tomorrow" (1999) and has been certificated Million for physical sales and Gold for digital sales by Recording Industry Association of Japan.