We have investigated the distribution of three ion channel transcripts, Na_V1.5, KChIP2 and Kir2.1, in the heart. Na_V1.5 is responsible for the Na⁺ current and thereby determines the upstroke of the action potential, KChIP2 increases the cell surface expression of K_V4 channels and thereby increases the transient outward K⁺ current, and Kir2.1 is responsible for the background inward rectifier K⁺ current, I_K,1, and thereby generates the resting potential. Rabbits (~1.5 kg) were humanely killed, the hearts rapidly excised, the sinoatrial node, atrioventricular node and ventricles dissected and frozen in liquid nitrogen, and the preparations cryosectioned. To investigate the distribution of the transcripts, in situ hybridization was carried out using ~400 nucleotide riboprobes. If present in a cell, transcripts were present in a ring around the nucleus (presumably corresponding to the rough endoplasmic reticulum). Na_V1.5 was: absent from the centre of the sinoatrial node, but present in the periphery of the sinoatrial node; present throughout the atria; absent from the inferior nodal extension, but present in the penetrating bundle (atrioventricular node); and present throughout the ventricles. KChIP2 was: present in the centre of the sinoatrial node, but curiously absent from the periphery of the sinoatrial node; present throughout the atria; absent from throughout the atrioventricular node; more abundant in the midmyocardium of the interventricular septum than in the periphery of the septum; and more abundant in the epicardium than in the endocardium of the left and right ventricular free walls. Kir2.1 was: curiously equally abundant in the sinoatrial node and surrounding atrial muscle; more abundant in the ventricles than in the atria; more abundant in the midmyocardium of the interventricular septum than in the periphery of the septum; and more abundant in the epicardium than in the endocardium of the left and right ventricular free walls. In conclusion, in situ hybridization reveals a highly complex distribution of ion channel transcripts in the heart; transcript abundance can vary both within a tissue (e.g. centre versus periphery of the sinoatrial node) as well as between tissues (e.g. sinoatrial node versus ventricle).