An apparatus for repairing a heart valve can comprises a leaflet-plicating mechanism configured to plicate a leaflet of a heart valve and a helical needle comprising a plurality of coils. The needle can be configured to implant a suture to extend helically through plicated tissue of the heart valve. The leaflet-plicating mechanism can comprise first and second leaflet-capture arms, which can be configured to move toward and away from each other between an open position and closed position. The leaflet-capture arms can be configured to plicate the leaflet as the leaflet-capture arms are moved from the open position to the closed position.