The present study investigates the role of F3 in the perception of valence of emotional expressions by using a vowel [a:] with different F3 values: the original, one with F3 either lowered or raised by 30% in frequency, and one with F3 removed. The vowel [a:] was extracted from the simulated emotions, inverse filtered and manipulated. The resulting 12 synthesized samples were randomized and presented to 30 listeners who evaluated the valence (positiveness/negativeness) of the expressions. The vowel with raised F3 was perceived more often as positive than the sample with original (p = 0.063), lowered (p = 0.006) or removed F3 (p = 0.066). F3 may affect perception of valence if the signal has sufficient energy in high frequency range.