KCNH3 is the pore-forming (alpha) subunit of a voltage-gated inwardly rectifying potassium channel. The channel is characterised by a fast rate of activation during depolarisation, followed by rapid inactivation at much more depolarised values. This produces inward rectification through a C-type inactivation mechanism. The channel also shows a rapid recovery from inactivation. These properties set KCNH3 apart from many other voltage-gated potassium channels and make it a useful subject for studies of channel gating.

The KCNH3 gene encodes a protein that localises to the cell membrane and is predominantly expressed in the forebrain. UniProt places it in the potassium channel family, H (Eag) subfamily, within the Kv12.2/KCNH3 sub-subfamily. HGNC classifies it in the groups of potassium voltage-gated channels and PAS domain containing proteins. Two transcript variants encoding different isoforms have been reported for the gene. Orthologues are annotated in mouse and rat as Kcnh3.

Studies in mice have found that cognitive function increases when the gene is knocked out, which has drawn interest to KCNH3 in neuroscience. In humans, the encoded protein has also been shown to bind glycoprotein 120 of the HIV-1 envelope. The gene was previously named potassium voltage-gated channel, subfamily H (eag-related), member 3, and the aliases Kv12.2, BEC1 and elk2 are still found in the literature. Researchers studying KCNH3 may use a KCNH3 antibody or KCNH3 ELISA kit to examine expression of the KCNH3 protein.