Medela Swing, electric pump with 2 phase expression.Like the Harmony and Pump in Style, the Medela Swing has 2-phase expression. This imitates the babys natural sucking rhythm. Initially babies suck rapidly to stimulate and induce milk let-down. This phase is called Stimulation. Once the milk starts flowing, they settle into a more relaxed sucking speed. This phase is called Expression. Small, effective and quiet Electric or battery powered