Lown-Ganong-Levine (LGL) syndrome is a preexcitation syndrome producing supraventricular tachycardia that is neither atrial fibrillation nor atrial flutter. This syndrome is characterized by a short P-R interval (<20 milliseconds) and normal QRS complexes.

The incidence of LGL syndrome is estimated to be approximately 0.5% worldwide.

Some evidence suggests that LGL is a hereditary condition in some families. No definitive structural/anatomic anomaly has been identified as yet. Many experts believe that LGL is not a syndrome itself, but a manifestation of any of several maladies.