Which animal can stop its heart beat for more than six months?

A much more complex strategy for winter survival is freeze tolerance, the ability to endure the actual formation of ice within the body. Ice forming in body tissues can do a lot of harm. Ice crystals can puncture small blood vessels, squeeze and deform cells to the point of breaking. And even if ice doesn't break into cells, it leads to their severe dehydration, for water is sucked out of cells into the growing ice crystals leaving behind a shrunken and damaged cell.  The Wood frog is one among the example, their soft, water-permeable skin is no barrier to ice and so, whenever frost penetrates into their winter home, they freeze. Ice penetrates though all of the fluid compartments of the animal and within just a few hours a mass of ice fills the abdominal cavity encasing all the internal organs. Large flat ice crystals run between the layers of skin and muscle, and the eyes turn white because the lens freezes. Their blood stops flowing and as much as 65% of the frog's total body water is converted to ice. Breathing, heart beat, and muscle movements all stop and the frozen frog exists in a virtual state till the winter period ends. The frog’s body once again comes into the normal state whenever the ice gets melt.