Pore-forming (alpha) subunit of a voltage-gated delayed rectifier (PubMed:10455180). Activates at more negative voltages, exhibits fast prepulse-independent activation kinetics and deactivates much more slowly, but shows no inactivation (By similarity). . This is the function of KCNH4 (potassium voltage-gated channel subfamily H member 4, Ensembl gene identifier ENSG00000089558).