Background: Cardiovascular disease killed 12.9 million people in 2010 [1]. A characteristic of cardiovascular disease is excessive sympathetic tone. Many investigators have studied this but few have explored parasympathetic sensory input to the brain from atrial volume receptors (AVRs). The AVR reflex arc is crucial in maintaining normal plasma volume. Fibres from these receptors convey information about central venous volume via the vagus nerve to the medulla and hypothalamus influencing vasopressin expression and sympathetic activity. Type A volume receptors fire during systole and type B during diastole [2]. The epithelial sodium channel (ENaC) is a major contributor to muscle spindle mechanosensory transduction in rat skeletal muscle [3]. In our study, we hypothesize that AVRs utilize ENaC for mechanotransduction of atrial stretch and that inhibition of ENaC using amiloride will inhibit these afferent signals. To test this, we administered amiloride to an in-vitro rat heart-vagal nerve preparation whilst recording afferent vagal action potentials. Methods: Adult male Wistar rats (body mass: 128-190g) were euthanised by cervical dislocation while under 5% isoflurane anesthesia. Mediastinal tissue was rapidly extracted and superfused with oxygenated Tyrode’s solution (pH7.4). The great veins were tied and a double-lumen catheter inserted into the right atrium via the tricuspid valve. The right atrium was pressurised under isovolumetric conditions and electrophysiological recordings were taken from the vagal nerves until cardiac units were isolated. Thereafter, 100µM amiloride hydrochloride was added to the tissue bath while vagal recordings continued. Recording and analysis was carried out using Spike2 (CED, UK). All experiments were conducted in accordance with local ethical committee approval and relevant licensing from regulatory authority. Data were analyzed with a paired Student’s test. Results: Twelve cardiac units were analyzed with phase histograms (one pressure peak to the next represents 0 to 360°). Five systolic (mean 48°, SD 49°) and 7 diastolic units (288°, SD 16°) were observed. In the pharmacological studies, mean cardiac interval was 368ms (SEM 54.43, n=4) and post 100µM amiloride was 356ms (SEM 43.29, n=4; p=0.74). Mean atrial pressure was 1.07 mmHg (SEM 0.25, n=4) and post 100µM amiloride was 1.07 mmHg (SEM 0.19, n=4; p=1.0). Cardiac vagal recordings were obtained in two of these studies. Amiloride had no effect in one study and reduced vagal firing rate in the other (7.9 Hz to 4.4 Hz). Conclusions: The rat atrium possesses both type A and type B AVRs. At 100µM, amiloride has no indirect effects on atrial contraction or rate of beating. This vagal-atrium preparation will permit a resolution of the role of ENaC in atrial mechanotransduction.