We study theoretically single-electron loss from the ground state of a heliumlike highly charged ion in fast collisions with an atomic particle (a nucleus or an atom), focusing on electron emission energies where the so-called excitation-autoionization channel of electron loss becomes of importance. The presence of this channel leads to the appearance of sharp structures in the energy distribution of the emitted electrons and may also noticeably influence the angular distributions of the emission in the vicinity of autoionization resonances. We performed calculations for electron loss from Ca18+(1s2) and Zn28+(1s2) in 100 MeV/u collisions with neon. It is shown that two qualitatively different subchannels (which involve either one or two interactions between the electrons of the ion and the incident atomic particle) substantially contribute to excitation-autoionization and take active part in the interference with the direct channel of electron loss; however, they practically do not interfere with each other. Our consideration also shows that the account of QED corrections is important for an accurate description of electron loss even from relatively light heliumlike HCIs.