Enables voltage-gated potassium channel activity involved in cardiac muscle cell action potential repolarization. Acts upstream of or within cardiac conduction; cardiac muscle cell action potential involved in contraction; and potassium ion export across plasma membrane. Located in membrane. Is integral component of postsynaptic specialization membrane. Is active in GABA-ergic synapse. Is expressed in heart and heart ventricle. Human ortholog(s) of this gene implicated in Brugada syndrome 9 and spinocerebellar ataxia type 19/22. Orthologous to human KCND3 (potassium voltage-gated channel subfamily D member 3). [provided by Alliance of Genome Resources, Apr 2022]