The main risk associated with elective cardioversion is the formation of a blood clot, which could dislodge and travel through the bloodstream as an embolus, potentially resulting in a stroke. Anticoagulant medications may be given before and after the cardioversion to reduce this risk.

Another way to minimize the risk of atrial blood clots is through the use of a transesophageal echocardiogram (TEE). This type of echocardiogram requires the patient to swallow a device (e.g., a transducer) that produces images of the heart from the inside of the body. It is an excellent strategy for determining whether or not blood clots are present in the atria. If none are present, then cardioversion can proceed without weeks of anticoagulant treatment. If a TEE cannot be performed it is advisable to be on an anticoagulant medication for two to three weeks.

There is also a risk that cardioversion can stimulate more dangerous arrhythmias. It is not uncommon for patients to experience temporary and non-threatening arrhythmias after cardioversion. However, if the timing of the shocks is wrong, there is a risk of ventricular fibrillation. Other abnormal heart rhythms that are associated with cardioversion include atrial arrhythmias, bundle branch block and bradycardia. Depending on the severity of the arrhythmia, treatment may be necessary. However, the frequency with which these problems occur is exceedingly low.