(a) A progressive increase of Aβ40 plasma levels was observed after the commencement of hypothermia reaching statistical significance 96 h after commencement of hypothermia, when compared to control patients. Differences were detected by one-way ANOVA followed by Tukey b test [F(5,42) = 7.30, **p < 0.01 vs. Control, HIE 0 h and HIE 6 h, ††p < 0.01 vs. HIE 0 h] (Control n = 7, HIE 0 h n = 11, HIE 6 h n = 8, HIE 24 h n = 10, HIE 72 h n = 8, HIE96 h n = 4). (b) A similar profile was observed when Aβ42 levels were analyzed [F(5,42) = 2.65, *p = 0.036 vs. HIE 0 h] (Control n = 7, HIE 0 h n = 11, HIE 6 h n = 8, HIE 24 h n = 10, HIE 72 h n = 8, HIE96 h n = 4). (c) Significant correlations were detected between time HIE patients spent under hypothermia (0–72 h) and Aβ40 (*p < 0.01) and Aβ42 levels (**p = 0.003).