Final answer:
After turning on the defibrillator, the next step is to analyze the patient's heart rhythm using the EKG monitor.
Step-by-step explanation:
The next step you should perform after turning on the defibrillator is to analyze the patient's heart rhythm using the electrocardiogram (EKG) monitor. This will help determine if defibrillation is necessary. The EKG will show whether the patient's heart is in ventricular fibrillation or another arrhythmia that requires electrical cardioversion.