To assess the short-term behavior of the right ventricle anterior papillary muscle extrasystoles (APME) based on Holter recording and exercise data, 20 subjects (age 31.5 +/- 13.7 years) with otherwise normal electrocardiogram were studied. APME was diagnosed when it resembled LBBB morphology, with downward oriented AQRS in the frontal plane, slurred r wave in lead V1, and an R/S ratio less than 1 in this same lead. Except for palpitations in ten patients, there were no other symptoms related to the arrhythmia. Two Holter recordings, 30 to 330 days apart, were performed and their results compared. In the first Holter recording, the average rate of VPB/minute was 9.9 +/- 2.5 (xg +/- SD). Half of the patients had couplets and five had ventricular tachycardia. In the second Holter recording, the average rate of VPB/minute was 8.7 +/- 3. In eight cases, couplets were recorded, in half of which one or more episodes of ventricular tachycardia were also noted. Six patients showed another VPB morphology distinct from APME. Stress test suppressed VPB in 10/13 patients, couplets in 2/3 and ventricular tachycardia in the only one with this arrhythmia at the start of the test. Repetitive forms vs APME frequency and vs heart rate exhibited an inverse relationship. We conclude that APME is a clinical condition with both high and stable VPB levels, which can be found in subjects with otherwise normal hearts and in the short-term has a spontaneous uncomplicated outcome.