Autonomic modulation of sinoatrial node cells (SANC) beating has long been characterized, but new methods of analysis can give further insights into this field. We studied the effect of acetylcholine (ACh, 10 nM) and isoproterenol (ISO, 100 nM) to spontaneously beating patch clamped guinea pig SANC. The analysis was performed with the new software Scaldyn, specifically designed to handle very long sequences of electrophysiological data. The program allows determination of a variety of measurements for each beat, including cycle length (CL), action potential (AP) duration (APD), slope of diastolic depolarization, maximum diastolic potential, AP amplitude, maximum rate of depolarization, and stores them in matrix form. Measurement definitions can easily be adjusted, and the entire sequences (up to 50-60 min), any part of them, or any graphic representation of parameters (i.e. phase plots, Poincarè plots) measured for arbitrarily chosen time frames can be simultaneously visualized. Apart from finding the expected significant changes induced by ACh/ISO on SANC APs, such as the increase/decrease in CL, increase/decrease in maximum diastolic potential, we studied dynamic restitution plots (DRP, APD of each beat vs preceding CL) for arbitrarily long (approximately 30 s) AP sequences in control condition and after application of the autonomic agonists. Whereas in control no significant correlation within DRP was detected (plots equally scattered along both axes), during ACh/ISO application the correlation between APD and preceding CL became significant, with ACh showing a lower restitution slope and higher temporal dispersion of CL, and ISO a much higher slope and higher temporal dispersion of APD.