The spelling of the surname "Heishman" can be explained using the International Phonetic Alphabet (IPA). The first sound is /h/, which is a voiceless glottal fricative. The next sound is /i/, which is a short vowel pronounced as "ih". The following sound is /ʃ/, which is a voiceless postalveolar fricative commonly pronounced as "sh". The last two sounds are /m/ and /ən/, pronounced as "m" and "ən" respectively. Therefore, the phonetic transcription of "Heishman" is /ˈhaɪʃmən/.