Potassium voltage-gated channel subfamily D member 3, also known as Kv4.3, is a protein that in humans is encoded by the KCND3 gene. KCND3 is a member of the potassium channel, voltage-gated, shal-related subfamily. Voltage-gated potassium (Kv) channels represent the most complex class of voltage-gated ion channels from both functional and structural standpoints. Their diverse functions include regulating neurotransmitter release, heart rate, insulin secretion, neuronal excitability, epithelial electrolyte transport, smooth muscle contraction, and cell volume. It is mapped to 1p13.2. KCND3 is important in membrane repolarization in excitable cells. It contributes to the cardiac transient outward potassium current (Ito1), the main contributing current to the repolarizing phase 1 of the cardiac action potential.