Group 1 will have 12 subjects enrolled in a 3-period, randomized, crossover to compare multiple doses of a 90-30 mg split-dose of the tolvaptan IR formulation, a 120 mg once daily (QD) dose of the tolvaptan MR formulation, and, in an incomplete block randomization, multiple doses of either 20 mg QD, 60 mg QD, or 20 mg twice daily (BID) tolvaptan MR formulation. All dose regimens will be administered for 7 days. Placebo doses will be administered in order to mask QD vs BID treatments.