This is some next-level, balagtasan-era Tagalog. Think of it as the poetic version of "chest" or "heart." It's not the physical organ, but the place where you feel that intense "dubdob" (fervor). When someone says "sa aking dubduban," they mean "in the depths of my heart/soul." It's so deep, you'd probably only hear it in a kundiman or a historical drama.