This classroom-based action research investigates the impact of teaching problem-solving heuristics on preservice teachers' mathematical creativity, self-efficacy, and problem-solving beliefs. The study was conducted with seven preservice teachers at a state university in the Philippines, using a Plan-Do-Study-Act (PDSA) cycle. Participants were assessed on their mathematical creativity in solving non-routine problems in terms of fluency, flexibility, and originality before and after the intervention. Results indicated a significant improvement in fluency, suggesting enhanced proficiency in tackling non-routine problems. However, gains in flexibility and originality were not statistically significant, highlighting the need for further practice and reinforcement. On the other hand, participants exhibited increased self-efficacy in mathematical creativity across all indicators. Despite these positive outcomes, their beliefs about mathematical problem-solving remained stable. The study underscores the importance of incorporating heuristic strategies into mathematics education to foster creativity and problem-solving skills, although extended and sustained efforts are required to develop flexibility and originality fully. These findings contribute to understanding practical pedagogical approaches for enhancing mathematical creativity, self-efficacy, and problem-solving beliefs through heuristic instruction among preservice teachers.