"Heuristic approach" is a teachers' professional development (TPD) method supported by principled practical knowledge (PPK) which focuses on principled practical guidance that develops teachers' capacity in innovative learning designs. This study reports the key features of the design and implementation of a TPD programme aimed at facilitating teachers' experiential learning in designing and implementing seamless inquiry science learning (SISL). The TPD is based on the notion of fast and frugal heuristics which are supported by PPK and lead to actual classroom action. Two teacher case studies were analysed to investigate the teachers' learning trajectory underpinned by an experiential learning framework throughout the TPD programme. As learners of innovative pedagogy, the teachers explored the design and implementation of SISL with their students. The findings indicate that the TPD programme had a positive impact on three aspects of teachers' experiential learning: (a) acquiring new pedagogy; (b) improving knowledge and skills in the seamless inquiry science lesson (SISL) design and implementation; (c) nurturing reflective practices in teachers concerning the designing and implementation of SISL lessons. The teachers' professional reflection and growth through experiential learning processes demonstrate how heuristic-based TPD engaged them as creative and professional lesson designers, resulting in meaningful changes in classroom practices. Our data analysis concluded that the heuristic-based TPD should be designed in such a way that it is authentic, reflective, practice-based and focused on meaningful tasks for the teachers.