What device is used to deliver electrical stimulus in defibrillation?

The defibrillator is the device specifically designed to deliver an electrical stimulus to the heart in order to restore a normal rhythm during potentially life-threatening heart arrhythmias, such as ventricular fibrillation or pulseless ventricular tachycardia. It works by delivering a controlled electrical shock to the heart, which can help to reset the electrical activity and re-establish a coordinated heartbeat.

In contrast, a pulsed ultrasound machine is used for imaging or therapeutic purposes but does not provide electrical stimulation for cardiac issues. A cardiac monitor is designed to continuously observe and display the heart's activity, but it does not have the capability to deliver electrical shocks. Similarly, a ventilator assists with breathing support and does not play a role in electrical cardiac stimulation. Hence, the defibrillator is the only correct choice for delivering electrical stimuli in defibrillation scenarios.