This study examines the perception of diphthongs and hiatuses in 11 heritage Spanish speakers and 6 Spanish-dominant bilingual speakers with an AXB discrimination task (Lukyanchenko, Anna & Kira Gor. 2011. Perceptual correlates of phonological representations in heritage speakers and L2 learners. In Nick Danis, Kate Mesh & Hyunsuk Sung (eds.), Proceedings of the 35th annual Boston University conference on language development, 414–426. Sommerville, MA: Cascadilla Press). In Spanish, diphthongs and hiatuses represent distinct vocalic sequences (Schwegler, Armin, Juergen Kempff & Ana Ameal-Guerra. 2010. Fonética y fonología españolas, 4th edn. Hoboken, NJ: Wiley). However, there are words in which the pronunciation of the vocalic sequence as either a diphthong or hiatus serves as a contrastive feature, as in the example of ley / leí (Face, Timothy L. & Scott M. Alvord. 2004. Lexical and acoustic factors in the perception of the Spanish diphthong vs. Hiatus contrast. Hispania 87(3). 553–564; Hualde, José I. & Mónica Prieto. 2002. On the diphthong/hiatus contrast in Spanish: Some experimental results. Linguistics 40(2). 217–234). Given that these features also exist in English, albeit in different forms, does L2 influence of English impact heritage Spanish listeners' perception of diphthongs and hiatuses in Spanish? Specifically, this study examines discrimination between the diphthong / hiatus as a contrasting feature with /a e o/ as the nucleic vowel in the diphthongs. Results indicate that there is not a significant difference in discrimination between heritage speakers and Spanish-dominant bilinguals. Additionally, the nucleic vowel in the diphthong tokens is a significant factor for the ability to discriminate diphthongs vs. hiatuses in heritage Spanish speakers. The findings of this study contribute to the corpus of phonetic studies focusing on heritage Spanish speakers and perception in their heritage language.