Atar means "to tie" or "to bind." While it can refer to physically tying something, it often carries a deeper, metaphorical meaning of restricting or controlling.
In Kalimba's song, he sings, "Pero a mi corazón no lo puedes atar" (But you cannot tie my heart). Here, atar beautifully conveys the idea that love and emotions cannot be controlled or restrained, making it a powerful and relatable word in the context of falling in love against one's will.
Kalimba spends this song losing an argument with his own heart. He opens flatly refusing to fall for someone — "No me quiero enamorar" (I don't want to fall in love) — then immediately admits the fight is already lost: "Yo no quería quererte" (I didn't want to love you) and "no lo pude evitar" (I couldn't avoid it). The chorus turns that resistance into surrender, since however hard he tries to stay guarded, "a mi corazón no lo puedes atar" (you can't tie down my heart). By the bridge he has stopped pretending discipline works at all, asking "Quién le puede explicar" (who can explain it to him) why kissing her keeps undoing him — "Porque al besarte me pierdo" (Because when I kiss you, I lose myself).