Isolated noncompaction of the left ventricular myocardium is a rare cardiac 
disorder due to an arrest in myocardial morphogenesis. It is characterized by 
prominent and excessive trabeculation in a ventricular wall segment, with deep 
intertrabecular spaces perfused from the ventricular cavity. Echocardiographic 
findings are important clues for the diagnosis. Clinical symptoms include signs 
of left ventricular systolic dysfunction even to the point of heart failure, 
ventricular arrhythmias, and embolic events. We describe an adult case in whom 
the only clinical symptoms were life-threatening ventricular arrhythmias. 
Transthoracic echocardiography did not contribute to the diagnosis, which was 
made thanks to left ventricular contrast angiography. Electrophysiological 
testing induced a fast monomorphic sustained ventricular tachycardia, with 
hemodynamic impairment, that was refractory to pharmacological treatment, and 
for this reason a permanent cardioverter-defibrillator was implanted. A 
subsequently performed transesophageal echocardiographic examination showed a 
localized, regional increase in left ventricular wall thickness and degree of 
trabeculation. The causes and electrophysiological mechanisms of arrhythmias in 
noncompaction are still unknown: grossly irregular branching and connecting of 
myocardial fascicles in the noncompacted segments, isometric contraction with 
increased wall stress, and localized coronary perfusion impairment can all 
induce disorganized or delayed activation and increase the potential for 
arrhythmias. This is the first reported case of noncompaction in which an 
implantable defibrillator was used to control life-threatening arrhythmias.