Final answer:
Cardioversion is a procedure to restore a normal heart rhythm by applying an electrical shock; in open-heart surgery, if the resistance is 500 ohms and a 10.0-mA current is needed, a 5 V shock is required. This use of brief, intense current is what restarts the heart's rhythm.
Step-by-step explanation:
Cardioversion and Defibrillation
Cardioversion is a medical procedure used to treat a heart that is beating irregularly or too fast. An electrical shock is applied to the heart to reset its rhythm back to normal. This process is also referred to as defibrillation when the heart is in a state of cardiac arrest due to arrhythmias like ventricular fibrillation. A device called a cardiac defibrillator delivers this shock. During open-heart surgery, the resistance of the path through the heart is often 500 ohms, and a 10.0-mA current is typically required to achieve cardioversion. To determine the voltage needed, one would apply Ohm's Law, which states that Voltage (V) equals Current (I) times Resistance (R), V = I * R. In this case, applying 10.0 mA across 500 ohms would necessitate a voltage of 5000 mV, or 5 V. Defibrillators use a brief but intense current that results in a brief but effective contraction of the heart, effectively 'rebooting' it.