when the incomplete left ventricle is right-sided The atrioventricular conduction tissues are bizarre when there is a solitary and indeterminate ventricle.29 Cardiac Position An unusual position of the heart should always raise the suspicion of isomerism The location of the heart, and the position of its apex, however, fail to discriminate between right and left isomerism Functional Cardiac Abnormalities Arrhythmias Arrhythmias can be present in those with either right or left isomerism, with 20% or more experiencing arrhythmias.30 This should be of no particular surprise considering the previous discussion of abnormalities present in the formation of the conduction system itself In those with right isomerism, the most frequent arrhythmia is supraventricular tachycardia, accounting for 85% of arrhythmias in this population In those with left isomerism, atrioventricular blocks represent the most common arrhythmias Of those with left isomerism who have an arrhythmia, 69% will have atrioventricular block The most frequent is first degree atrioventricular block, which is noted in 32% of those with left isomerism and arrhythmias Second degree atrioventricular block is noted in 12% of those with left isomerism and arrhythmias, while complete atrioventricular block is noted in 26% A junctional rhythm is noted in 12% of those with left isomerism and an arrhythmia Onset of arrhythmia does not seem to differ between those with right or left isomerism with age of onset generally between 3 and 4 years of age A majority (80%) of arrhythmias in children with isomerism who develop arrhythmias will occur by 5 years of age When ablations are attempted in these patients, they are generally successful even despite difficulties related to systemic venous anomalies in these patients Implanted pacemakers are necessary in approximately 6% of those with right isomerism and 13% of those with left isomerism.30–47 Anecdotally, those with left isomerism who develop sinus or junctional bradycardia can be safely monitored without need for pacing as long as the rhythm is hemodynamically tolerated Children can thrive with such bradycardia with avoidance of the potential complications afforded by an implanted pacemaker While prophylactically leaving leads without a pacemaker generator at the time of a scheduled surgery may initially seem like a useful proposition in these patients, it should be avoided Such “jailed” leads can be problematic when magnetic resonance imaging studies need to be conducted due to manufacturer concerns of overheating Although there are several reports of patients with “jailed” leads who successfully and safely undergo such imaging studies, it can add to the overall concern of the imager and ancillary staff, subsequently causing such studies to be delayed or even entirely avoided Myocardial Fibrosis and Myocardial Infarction Necropsy studies of hearts from those with isomerism demonstrate myocardial fibrosis in 16% with frank ischemia in 10% of specimens from those with isomerism It is unclear as to how these findings may translate into issues with ventricular function in the future and is also unclear how these findings may impact myocardial infarction in adults with isomerism.48 A study on adults with myocardial infarction demonstrated that while there were differences in the location of infarcts in those with isomerism that age, ability to stent and mortality because of myocardial infarction did not differ between those with or without isomerism.49