Preparation

The frog is double-pithed, a procedure which destroys the brain and spinal cord. This effectively denervates the heart, which will however continue to beat for some time, provided it is kept moist with Ringers - a solution of electrolytes similar to the extracellular fluid. Throughout the experiment it is essential that both the heart and the skin of the frog are kept moist with Ringer's solution, since the latter is an important respiratory surface.

The frog is laid, ventral surface uppermost, on a corkboard and the skin removed from the pectoral region. The exposed xiphisternum is then removed creating a window in the body wall allowing the heart to be observed in the thorax. The pericardium surrounding the heart is cut away and the heart exposed.