Six hours of SD at the beginning of the light phase directly preceding T2 impairs spatial pattern separation performance (d2 values as mean + SEM) as measured with the OPS test (position 3; 24 h interval). A two‐factor repeated measures ANOVA, using Sleep Deprivation (non‐sleep deprived, sleep deprived) and Treatment (vehicle, vardenafil) as within subject factors, showed no significant interaction effect (F(1,11) = 4.138, p = NS; N = 12), but a main effect for Treatment (F(1,11) = 8.042, p = .016; N = 12), indicating that vardenafil protects against SD‐induced deficits in spatial pattern separation. Additionally, a direct statistical comparison of the “vardenafil SD” and “vehicle SD” groups results in a significant difference (p = .009; paired samples t test). # represents a significant difference from zero (# = p < .05, ## = p < .01) using independent samples t test. NSD = non‐sleep deprived; OPS = spatial object pattern separation task; PDE4‐I = phosphodiesterase type 5 inhibitor (vardenafil); SD = sleep deprived; T1 = learning trial; T2 = test trial; Veh = vehicle.