George Ralph Mines was a pioneering English cardiac electrophysiologist. He made two important contributions to cardiac electrophysiology. First, he proposed that an action potential wave front could propagate in a circle, repeatedly activating the tissue. Second, he discovered the vulnerable period of the heart: the time during the cardiac cycle when a single stimulus can induce ventricular fibrillation. On November 7, 1914, Mines was found unconscious in his laboratory, and died later that day. His death may have been caused by self-experimentation using electrical stimuli.