To determine the effect of varying the duration of electrocardiographic recording on the detection of high premature ventricular complex (PVC) rates (30 or more PVCs/hour) and/or complex PVCs (multiform PVCs, couplets or runs) in survivors of myocardial infarction, we evaluated 175 24-hour ECG tapes with such arrhythmias for their occurrences detected in the first 1, 2, 6, 12 and 18 hours of the recordings. The first hour of recording disclosed only 47% of the tapes that, over 24 hours, showed high PVC rates or complex PVCs or both, whereas 6 hours of recording uncovered 89% of the tapes with these arrhythmias. Although a 12-hour ECG recording uncovered only 84% of the tapes with couplets and 75% of those with runs, it identified 92% of the tapes with high PVC rates and/or complex PVCs. The detection rate of high PVC rates or complex PVCs is logarithmically related to the recording duration. Seventy-eight percent of the tapes that had complex PVCs and peak PVC rates greater than 100 beats/hour, and 63% of the tapes with these complex PVCs and peak PVC rates of 30-100 beats/hour, showed these complex PVCs in the first hour. In contrast, only 22% of the tapes with complex PVCs and peak PVC rates less than 30 beats/hour were identified during the same interval. We also found that the average number of PVCs/hour was slightly higher in the first than the last 12 hours of the tapes (51 vs 43 PVCs/hour). This study demonstrates that (1) the detection rate for complex PVCs during the first hour of recording is related to the peak PVC rate, (2) a 12-hour recording during the waking period is sufficient to identify most survivors of myocardial infarction who have high PVC rates and/or complex PVCs, and (3) the detection of tapes with high PVC rates or complex PVCs can be predicted from its logarithmic relationship with the recording duration.