Repetitive 10-hour ECG recordings of 289 patients obtained within a year after myocardial infarction were analyzed for the presence of ventricular runs, and their association with various types of ventricular ectopic activity (VEA), average rate of premature ventricular complexes (PVCs), and coupling interval of PVCs initiating the runs. Tapes which contained complex VEA (bigeminy, multiform PVCs, couplets, or runs), early PVCs (coupling interval < 400 msec), or late PVCs (coupling interval > 600 msec) had a substantially higher average PVC rate than those without them. The occurrence of ventricular runs was significantly more likely in tapes having other complex VEA or late PVCs than in those without them, and when tapes were stratified by PVC rates the presence of these dysrhythmias appeared to have an independent predictive value for the occurrence of runs. In contrast, the influence of early PVCs on the occurrence of runs was rather minimal, and this seemed to be related to their common association with the PVC rate. Furthermore, a larger percentage of isolated PVCs had coupling intervals between 400 msec and 600 msec, and most couplets (77%) and runs (67.8%) were initiated by PVCs with coupling intervals in this range. However, the proportion of either short (< 400 msec) or long (> 600 msec) coupling interval PVCs initiating couplets or runs was significantly higher than those with intermediate coupling intervals (between 400 and 600 msec).