In 1899, Jean-Louis Prévost and Frédéric Batelli published in the Comptes Rendus de l'Académie des Sciences the discovery that a high-voltage electric shock could reverse ventricular fibrillation in mammalian hearts, restoring normal rhythm. Building on McWilliam's work (1889), which had shown how electricity induced VF, Prévost and Batelli demonstrated the other side of the phenomenon: a more intense current reversed the electrical chaos. This is the fundamental biological principle underlying all later defibrillation technology. Beck (1947) applied it in humans with open chest; Zoll (1956) extended it to closed chest.