Dysfunction of the cardiac potassium channel, IKs, can lead to the prolongation of the QT interval in the electrocardiogram, a potentially life-threatening condition known as the long QT syndrome (LQTS). The IKs consists of a pore-forming subunit, encoded by KCNQ1, and an auxiliary subunit, encoded by KCNE1. One of the most common mutations associated with the inherited form of LQTS is the substitution of an alanine residue to a valine at position 341 in KCNQ1. In the present study, we investigated the impact of the KCNE1 subunit on the A341V mutant. The whole-cell patch clamp technique was used to record current from transiently transfected HL-1 cells, a cardiac cell line derived from mouse atrial cells. In contrast to the non-functional A341V, the cotransfection of A341V with KCNE1 (A341V+KCNE1) resulted in a functional channel. Though the resultant current was qualitatively similar to that of native IKs, A341V+KCNE1 resulted in a significantly smaller mean current density, longer time to half-activation and a rightward shifted voltage dependence of activation with a steeper slope than the wild-type KCNQ1+KCNE1. To determine whether the observed functional restoration of A341V by KCNE1 involved trafficking of the mutant construct, HL-1 cells were transfected with a GFP-tagged A341V with and without KCNE1 and visualized by confocal microscopy. No differences in the expression pattern of A341V in the absence or presence of KCNE1 were observed. Thus, the partial functional restoration by KCNE1 was not due to trafficking of A341V to the sarcolemma. To confirm that KCNE1 functionally rescued A341V, a mutant KCNE1, T58A that prevents the interaction of KCNE1 with KCNQ1, was cotransfected with A341V. T58A was unable to functionally restore A341V. Our studies showed an intriguing ability of KCNE1 to functionally rescue an LQTS-associated KCNQ1 mutant.