{Reference Type}: Case Reports {Title}: Is narrowest QRS the best? A case of cardiac resynchronization therapy in a patient with left anterior fascicular block. {Author}: Shimeno K;Tamura S;Hayashi Y;Abe Y;Naruko T; {Journal}: Pacing Clin Electrophysiol {Volume}: 46 {Issue}: 2 {Year}: 02 2023 {Factor}: 1.912 {DOI}: 10.1111/pace.14585 {Abstract}: The efficacy of cardiac resynchronization therapy (CRT) in patients with a narrow QRS duration has not been established. We present a patient with a narrow QRS duration and left anterior fascicular block in which CRT was effective. Left ventricular lead implantation at the optimal site and appropriately-timed left ventricular pacing (LVP) resulted in left ventricle reverse remodeling. Left ventricular dyssynchrony did not improve with LVP at a timing that resulted in narrower QRS than an intrinsic QRS duration. The optimization of LVP timing in CRT for patients with a narrow QRS duration is discussed.