Ringer's solution is a solution of several salts dissolved in water for the purpose of creating an isotonic solution relative to the body fluids of an animal. Ringer's solution typically contains sodium chloride, potassium chloride, calcium chloride and sodium bicarbonate, with the last used to balance the pH. Other additions can include chemical fuel sources for cells, including ATP and dextrose, as well as antibiotics and antifungals.
Ringer's solution is frequently used in in vitro experiments on organs or tissues, such as in vitro muscle testing. The precise mix of ions can vary depending upon the taxon, with different recipes for birds, mammals, freshwater fish, marine fish, etc.
Ringer's solution is named after Sydney Ringer, who in 1882–1885 determined that a solution perfusing a frog's heart must contain sodium, potassium and calcium salts in a definite proportion if the heart is to be kept beating for long.