This thesis sought to explore whether attention could influence trustworthiness evaluation of faces in a cardiac-gated manner. The attentional boosting effect describes a facilitated processing of visual stimuli that are presented concurrently with target stimuli. Furthermore, fearful faces presented during the systolic phase of the cardiac cycle are detected more easily and rated as more intense relative to those presented during the diastolic phase. There has been little work regarding the influence of attention (i.e. attending or ignoring a stimuli) on emotional valence embedded within the context of cardiac timing. This study examined how attention may modulate trustworthiness in face evaluation and whether this effect differs depending on the natural phasic pattern of the cardiac cycle. Participants performed a letter detection task, in which computer-generated face stimuli varying on three trust levels (low, neutral, high) obtained from the Social Perception Lab at Princeton University were concurrently presented with a target or distractor letter. The face-letter paired stimuli were time-locked to coincide with the systolic or diastolic phase of the participant’s individual heartbeat, followed by a subjective rating task of the preceding face. Results showed that while cardiac timing did not seem to influence subjective rating, faces that were paired with target letters were overall rated as more trustworthy than faces paired with distractor letters. This effect was significantly greater in neutral relative to low-trust faces, suggesting that simultaneously attending to an unrelated target letter added, rather than enhanced, positive valence to an intrinsically neutral face. A follow-up study was then conducted to determine whether the attentional manipulation was affecting perceptual salience rather than facial trustworthiness. The study used faces from the same database as the aforementioned experiment, again time-locked to systolic and diastolic phases. A short-term memory task was added to follow the target detection task, in which participants assessed whether a second face that was presented was the same or different from the immediately preceding face. Results indicated that neither attention nor cardiac cycle significantly affected participants’ performance in the short-term memory task. Our studies provide initial support for an attentional boosting effect in trustworthiness of faces, whereby attending to an unrelated target could generate positive valence that is not inherently present in a background face.