GSK2336805 is a hepatitis C virus NS5A inhibitor in clinical development for the treatment of chronic hepatitis C virus infection. This was a single-center, randomized, double-blind, placebo-controlled, two-period crossover study in healthy adults to evaluate the effects of a single 150-mg dose of GSK2336805 on echocardiographic measures of contractility. GSK2336805 had no effect on ejection fraction, and there was no significant correlation between GSK2336805 plasma concentration and ejection fraction. (This study has been registered at Clinicaltrials.gov under registration no. NCT01424540.).