4 Ezra’s notion of an “evil heart” is often cited as an illuminative Jewish parallel to Paul’s description of sin. However, it is necessary to understand how the evil heart is presented in 4 Ezra before it can be considered exegetically helpful for understanding the notion of sin in Paul’s and in other New Testament writings. To meet this need, the present article observes the ways in which the term evil heart is used in 4 Ezra, and concludes that in 4 Ezra, the evil heart has five distinguishable characteristics. Written in the wake of the Second Temple’s destruction, 4 Ezra seeks to understand the reasons for this tragic event, and identifies the evil heart, which can be characterized by the following five ways, as an evil force responsible for Israel’s downfall. First, it originates from the time of Adam. More specifically, the evil heart was formed in Adam, inclining him to sin, but it acquired universal potency to cause Adam’s descendants to fall, only as a result of Adam’s transgression. Second, its power is not deterred by Israel’s law because the evil heart made Israel fall no less than the rest of Adam’s descendants despite Israel’s possession of the law. Third, while the evil heart has universal potency, its power can be overcome by a small number of Israel’s remnants who are helped by God to resist it. Fourth, the evil heart, through Adam’s fall, brought universal mortality to Adam’s descendants, and also led Adam’s descendants, except for the remnants, to be in miserable postmortem existence and tragic eschatological separation from God. Fifth, the remnants who are immune to the corrupting power of the evil heart are considered a new Adamic people to inherit the new world and live in the new age, whereas the rest of Adamic humanity remain bound within the present world and will perish with it. These five features of the evil heart need to be in view whenever this notion is compared with supposed New Testament parallels.