That is a "defibrillator".
A 'defibrillator' is an electrical device that provides a shock to the heart when there is a life-threatening arrhythmia present.
'Defibrillation' is a process in which a defibrillator gives an electric shock to the heart. This helps reestablish normal contraction rhythms in a heart having dangerous arrhythmia or in cardiac arrest.
In recent years small portable defibrillators have become available, these are called automated external defibrillators or AEDs.
See Guidelines for CPR and Automated External Defibrillators at WebMD.
Tip! Find out How Can Death Due to Sudden Cardiac Arrest Be Prevented at National Heart, Lung, and Blood Institute.