The Lief is the world’s first ECG smart patch that helps retrain your response to stress with biofeedback. When your heart shows signs of stress, the Lief uses vibrations on the body to guide your breath with your heart’s natural rhythm in realtime. No screens needed. Just breathe with it. The Lief measures your heart rate variability (HRV) to recognize your stress patterns with clinical-grade accuracy. The Lief allows you to improve your HRV by breathing with your heart’s intrinsic rhythm. This resonant breathing exercise, known as HRV biofeedback, is a simple and safe way to amplify your HRV wave.