This will be a randomized, placebo-controlled, single, oral dose, four-way Williams crossover study design in healthy male and female subjects. The study consists of screening (28 days), treatment (1 day/dosing session) and follow-up (7 to 14 days) period and the total duration of study participation for each subject will be approximately 9 weeks. Each subject will participate in 4 dosing sessions separated by a minimum 7-day washout period. All subjects will receive single doses of retosiban 100 mg, (treatment A) retosiban 800 mg (Treatment B), moxifloxacin 400 mg (Treatment C) and placebo (Treatment D) in one of the four treatment sequences (ABDC, BCAD, CDBA, DACB) following a Williams design Twelve-lead ECGs and continuous Holter monitoring, clinical laboratory safety tests, vital sign measurements, physical examinations, adverse event reports, and pharmacokinetic samples will be collected throughout the study. In each study period, cardiac conduction will be measured using a 24-hour continuous 12-lead Holter monitor from the morning of Day 1 (dosing) until the morning of Day 2.