The study, published in Anesthsiology, says hydrogen sulfide gas carefully administered to mice induced a safe and reversible depression of nearly 50 percent of heart rate -- a suspended animation-like state -- without a drop in blood pressure, no change in blood oxygen levels and without a reduction in body temperature.

"Hydrogen sulfide is the stinky gas that can kill workers who encounter it in sewers; but when administered to mice in small, controlled doses, within minutes it produces what appears to be totally reversible metabolic suppression," study senior author Dr. Warren Zapol of Massachusetts General Hospital says in a statement. "This is as close to instant suspended animation as you can get, and the preservation of cardiac contraction, blood pressure and organ perfusion is remarkable."

Normal mice exposed to low-dose hydrogen sulfide were monitored for cardiac function and blood gas levels. While some mice were studied at room temperature, others were kept in a warm environment -- about 98 degrees Fahrenheit -- to prevent their body temperatures from dropping.