This article presents author's modest attempt to establish the Heraclitean meaning of the word 'aion' in the fragment B52 (Diels-Kranz). In his view the very starting-point presupposes a meticulous, unbiased analysis of relevant aphorisms of the Ephesian sage, and of the corresponding testimonies. A synoptic scrutiny indicates that Heraclitus hold a clear and original view on the eternity. The god of his philosophy - identified with one and common world - is eternal not only in his 'material' aspect as 'pur aeizoon' ('an ever-living fire', B30), but also in his 'rational' aspect as 'Logos eon aei' ('Logos existing always', B1). These assumptions lead him to employ a name for God which was destined to make a memorable career: 'Aion' ('He Who Always Is').