This study is a prospective, randomised, open-labeled, 6-sequence, 3-period, 3-treatment, crossover, and single-center clinical trial. A total of 30 healthy male volunteers will be enrolled and randomised into one among 6 groups (5 subjects per a group). The safety and PK/PD characteristics of co-administration of Clomipramine HCl and Sildenafil citrate will be investigated closely compared to the effects after single dose administrations.