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The early repolarization (ER) pattern is associated with sudden death and has been shown to be heritable. Its significance when identified in families affected by sudden arrhythmic death syndrome (SADS) remains unclear.We analyzed 12-lead ECGs of 401 first-degree relatives of individuals who had died from SADS. The prevalence of ER patterns was compared with family-clustered controls. ER was more common in SADS family members than in controls (21% versus 8%; odds ratio: 5.14; 95% confidence interval, 3.37–7.84) independent of the presence of a familial cardiac diagnosis. Both ascending and horizontal ER patterns were more common. In addition, ER was investigated for associations with findings from ajmaline provocation (n=332), exercise ECG (n=304), and signal-averaged ECG (n=118) when performed. ER was associated with a trend toward late depolarization, in general was suppressed with exercise and was unaffected by ajmaline. Inferior and horizontal patterns were, however, more likely to persist during exercise. Augmentation of ER with ajmaline was rare.The ER pattern is more common in SADS family members than controls adjusted in particular for relatedness. The increased prevalence is irrespective of ER subtype and the presence of other inherited arrhythmia syndromes. ER may therefore represent an underlying heritable arrhythmia syndrome or risk factor for sudden death in the context of other cardiac pathology. The differing response of ER subtypes to exercise and ajmaline provocation suggests underlying mechanisms of both abnormal repolarization and depolarization.