This is a randomized, placebo controlled, four period incomplete block,crossover thorough QT study to estimate the effect of repeat dose GSK573719/GW642444M (Vilanterol) combination and GSK573719 monotherapy on the QTc interval in healthy male and female subjects compared with placebo. At least 100 subjects will receive, four of five possible, 10-day repeat dose treatments. Treatments are placebo with a moxifloxacin placebo on day 10, placebo with moxifloxacin (400mg) on day 10, GSK573719/Vilanterol combination (125/25μg) with moxifloxacin placebo on day 10, GSK573719/Vilanterol combinatio (500/100μg) with moxifloxacin placebo on day 10, or GSK573719 (500μg) with a moxifloxacin placebo on day 10. All treatments are double blind except for moxifloxacin (400mg) and moxifloxacin placebo controls, given as a single-blind single dose on Day 10 of the appropriate treatment period.