Self-described as their most romantic song yet, Marineros' "El lado oscuro de tu corazón" is an instantly affecting ballad. After many singles of blending a tough, guitar-heavy (or just heavy) sound to pit against Constanza Espina’s delicate voice, the duo have softened their technique. Oneiric beats float in and out as melodic guitar lines sweep in to complete the picture, leaving a feeling of warmth. And yet, buried into its lyrics is also lingering pain of failed romance, and so the song is really classic Marineros as we’ve come to know them over the years. Bittersweet to the end, and made for deep backseat reflections. Marineros remain a treasure in the new class of Chilean pop.