Persistence of arrhythmia exercise response in healthy young men. This study assesses the persistence of arrhythmia at rest or during exercise tests, or both, after a mean follow-up period of 6.7 years in 76 young men (mean age 21.5 years) without evidence of organic heart disease. The exercise test was performed using a near-maximal protocol based on progressively increasing intermittent work loads, each of 5 minutes' duration. The initial work load was 50 W. The electrocardiogram was continuously registered throughout all stages of the examination. Arrhythmia was defined as the occurrence of greater than or equal to 1 supraventricular or 1 ventricular premature beat at any stage of the examination. At the follow-up examination, the rate of persistence of arrhythmia did not differ significantly among the subgroups, irrespective of follow-up interval, type of arrhythmia, or arrhythmia patterns of response to exercise. Two-dimensional echocardiography did not show any structural abnormalities and Doppler examination did not demonstrate significant abnormal flow patterns. Our data show that almost all patients continued to present arrhythmia after the follow-up period, without any evidence of development of organic heart disease. Moreover, the arrhythmia pattern of response to exercise remained constant throughout the years. At this time, arrhythmia without underlying heart disease seems to be of a benign natural course in these young men. 