While single PF cells from Nkx2-5 happloinsuficient mice display normal electrophysiological properties, ventricular conduction defects such as prolonged QRS duration, conduction blocks, and inducible ventricular arrhythmias have been correlated with a reduced PF network lacking ellipsoidal structures16–18. The gene discussed is NKX2-5; the disease is Ventricular arrhythmia.