The fastest way to melt an ice cube is to transfer heat energy to the ice as quickly as possible. Heat sources such as hot water, fire and an oven quickly melt ice, as does setting ice out in the sun.
At room temperature, an ice cube melts in about two hours. Another method used to melt ice besides heating it is by salting it, as is done on icy roads. Ice can be melted in about 15 minutes using natural salts. Salt causes ice to melt by disrupting the balance of the freezing point of the ice.