Usually the "heart shaped stop" was in fact meant to be paired with a clamp that had a sort of "diamond" or lozenge shape to the clamp, like your classic Campy NR, and the copies. In that case one of the clamp "points" fits right into the cleft of the Heart, sort of like a song lyric....I also never saw a stop for a BB cable guide like this Campania has, but I think this clamp is too "high and forward" on the down tube so your RD cable is riding high, just move the guide down nearer to the BB/DT joint: all will be fine