There are no reliable criteria for the evaluation of acute effects after oral application of a high single dose of an antiarrhythmic agent from the analysis of data of 46 patients with frequent complex VPBs suffering from severe organic heart disease (19 CHD, 27 COCM), we developed a new statistical model. Our calculations were based on nine 10 h Holter ECGs (2 controls, 1 placebo test, 6 class 1 antiarrhythmic agent tests) and two 24 h Holter ECGs (1 control, 1 while on chronic treatment) recorded in each patient. Usually reductions in VPB frequency caused by the medication occurred within 1 hour after application and lasted greater than or equal to 4 hours. The VPB reduction in the course of time was assessed by the parameters r and R (r = VPB reduction of the 4 h interval in comparison to the last hour before application, R = VPB reduction of the 4 h interval in comparison with an analogous interval of a control day). Values of r and R greater than or equal to -50% were never observed simultaneously. In contrast, the majority of all patients developed r and R values greater than or equal to -50% after application of an antiarrhythmic agent, and were classified as responders. As shown at a Holter control after 1 week of chronic treatment, the predictive value of a positive test result was good.