Two new C20-diterpenoid alkaloids, named gyalanunines A–B (1–2), were isolated from the whole plant of Delphinium gyalanum C. Marquand & Airy Shaw. Gyalanunine A was a rare C20-type diterpenoid alkaloid, which possess a hemiacetal ring linking C-2 to C-19. Structures were identified by multiple spectroscopic analyses including 1D and 2D NMR, IR, HR-ESI-MS, single-crystal X-ray diffraction methods. All compounds were tested for cardiotonic activity by isolated frog's hearts perfusion, and 1 exhibited appreciable cardiotonic activity. Preliminary mechanism of action studies indicated that the cardiotonic effect of 1 should be related to the β receptor. © 2022 Elsevier Ltd