Experiments were made on preparations of the rabbit right atrium maintained at 37 °C in oxygenated Krebs–Henseleit solution. Baseline diastolic transmural pressure was held at 2 mmHg. A step increase in diastolic pressure was accompanied by an immediate and rapid increase in atrial rate (fast response), followed by a slower increase (t1/2∼0.5 min) (slow response). The slow response to pressure steps was graded, approaching a maximum increase after a 12 mmHg step (44±4 min‐1from a baseline of 196±5 min‐1; mean±SEM;n=7;P<0.01). In preparations where baseline atrial rate had been reduced 50% by application of carbamylcholine, the slow response to an increase in pressure was augmented (n=7;P<0.01); an increase of 55±9 min‐1for a 12 mmHg step in atrial pressure. In preparations where baseline rate had been increased 63% by the application of isoprenaline, the slow response was attenuated (n=5,P<0.01), an increase of 22±7 min‐1for a 12 mmHg step. During sinusoidal pressure forcing (0.002–1.0 Hz), rate responses of control and carbamylcholine‐treated preparations had a high gain at frequencies 0.02 Hz. Carbamylcholine‐treated preparations also showed a high gain at frequencies 0.2 Hz. There appear to be two distinct intrinsic responses to changes in right atrial pressure; a rapid response which is augmented by cholinergic stimulation, and a slower response which is augmented by cholinergic stimulation and reduced by