The prevalence and type of arrhythmias has been studied in a representative sample of 2000 A thenians, aged 18–81 years, who underwent exercise testing on a treadmill according to the Bruce protocol. It was found that 121 persons (mean age 55.7±14.9 years, 31% > 65 years), exhibited arrhythmias on the ECG during either the exercise or the 10 min period following it (prevalence 6.05%). The age-adjusted prevalence was 6.7%, that is 7.1% for men and6.2% for women. Out of these 2000 Athenians 43 (2.15%) exhibited unifocal VPCs(23 with ≥ 3 VPCs min−1 and 20 with < 2 VPCs min−1), 10 (0.5%) multifocal VPCs (6 with single and 4 with paired VPCs), 12 (0.6%) bigeminy, 25 (1.25%) supraventricular PCs, 16 (0.8%), supraventricular PCs and VPCs, 5 (0.25%}respiratory arrhythmia, 3 (0.15%) coronary sinus rhythm, 3 (0.15%) atrialfibrillation, one (0.05%) ventricular tachycardia, 2 (0.1%) first-degree and one (0.05%,) second-degree A V block. In 32 out of those 121 persons arrhythmias were present also at rest (26.5%). Ventricular premature contractions and/or supraventricular PCs were the most common type of arrhythmias (87.6%,). The majority of VPCs (69%) and supraventricular PCs (80%) appeared during the 10-min observation period following exercise. Coronary heart disease and valvular heart defects were found more frequently among the participants with than those without arrhythmias at exercise testing (19.83%, vs. 8.83% and 2.48%, vs. 0.27%, respectively).