Since the beginning of the 21st century, heritage language studies have drawn unprecedented attention from language-related research areas. Despite the flourishing research on heritage language learning, relatively few studies have examined the motivational profiles of L1 English speakers engaged in heritage language learning. Theoretical explorations of heritage language learning motivation over the past decade have been largely informed by L2 motivational self guides, leading to the development of two closely related concepts: the "rooted L2 self" and the "indigenous heritage self," in which emotional connections to heritage history and the language maintenance and revitalization obligations are deemed prominent motivational forces. However, the cognitive mechanism underlying the two self concepts remains unclear. Moreover, how well the two heritage-related concepts account for L1 English speakers' motivation to learn a diminishing heritage language requires further investigation. This paper proposes that (1) Norton's "investment theory" could be applied to explain the cognitive processes underlying the heritage convictions of the rooted L2/indigenous heritage self; (2) the "ideal multilingual self" may generate motivational force to learn a heritage language as part of an internalized identity of rejecting monolingualism.