Abstract We investigated linguistic knowledge of subjunctive mood in heritage speakers of Spanish who live in a long-standing English-Spanish bilingual community in Albuquerque, New Mexico. Three experiments examine the constraints on subjunctive selection. Experiment 1 and Experiment 2 employed pupillometry to investigate heritage speakers’ online sensitivity to the presence of the subjunctive with non-variable governors (Lexical conditioning) and with negated governors (Structural conditioning). Experiment 3 employed an elicited production task to examine production of subjunctive in the same contexts. The findings of the heritage group were compared to those of a group of Spanish-dominant Mexican bilinguals. Results showed that in comprehension and production, heritage speakers were as sensitive as the Spanish-dominant bilinguals to the lexical and structural factors that condition mood selection. In comprehension, the two groups experienced an increased pupillary dilation in conditions where the indicative was used but the subjunctive was expected. In addition, high-frequency governors and irregular subordinate verbs boosted participants’ sensitivity to the presence of the subjunctive. In production, there were no significant differences between heritage speakers and Spanish-dominant bilinguals when producing the subjunctive with non-variable and negated governors.