From Wiktionary, the free dictionary
The imperative of heyra (“hear”).
heyrðu
- hey! oy! (used to grab attention)
- used when switching to another topic; right, so
- Heyrðu, ætluðum við ekki í sund? ― Oh hey, hadn't we planned to go swimming?
heyrðu
- third-person plural past active indicative of heyra