Invasive electrophysiological study. A, Measurements of sinus node recovery time (SNRT): exemplary ECG recordings obtained during atrial pacing at 100 ms paced cycle length and immediately upon termination of electrical stimulation. Triangles indicate stimulus artifact. Note delayed recovery of sinus rhythm in the db/db mouse. B, Corrected SNRT (CSNRT) was obtained by subtracting the sinus cycle length from the SNRT and was significantly prolonged in db/db mice. C, Atrioventricular (AV) Wenckebach periodicity, measured as the shortest paced cycle length allowing conduction of electrical impulse from atria to ventricles, remained unchanged in db/db mice. D, Ventricular effective refractory period (VERP), measured by extra-stimuli technique as the longest paced cycle length that did not elicit a propagating response, was indistinguishable in db/+ and db/db mice. *, P < 0.05, Student’s t-test. Number of animals is indicated in parentheses. The SNRT and AV Wenckebach period were not obtained in 1 db/+ and 1 db/db mouse, respectively, due to technical difficulties.