OBJECTIVE To clarify whether electrocardiographic (ECG) changes can be identified during a migraine attack and to determine whether there are ECG differences between periods with and without headache. BACKGROUND The clinical signs and symptoms of migraine point to involvement of the autonomic nervous system, and especially to disrupted regulation of the circulatory system and autonomic balance. This disruption may be more marked during a migraine attack. During a migraine attack, autonomic imbalance within the heart and its vessels conceivably may result in ECG abnormalities. METHODS In 30 patients with migraine, the ECG variables of heart rate, abnormalities of rhythm, PR interval, QRS duration, corrected QT interval, T inversion, and ST-segment changes were recorded during migraine attacks and pain-free periods. RESULTS Of the 30 patients studied during a migraine attack, 9 (30%) had one or more abnormalities of rhythm (including sinus arrhythmia, atrial premature contraction, and ventricular premature contraction), 20% had PR intervals greater than 0.20 seconds, 40% had corrected QT intervals greater than 0.44 seconds, 66% had T inversion, and 40% had ST-segment abnormalities. No patient had arrhythmia, PR intervals greater than 0.20 seconds, or corrected QT intervals greater than 0.44 seconds during a pain-free period. No differences were noted for ST-segment changes, T inversion, and total ECG changes between periods with and without headache, but both PR and corrected QT intervals were significantly longer during migraine attacks than during pain-free periods. CONCLUSIONS We conclude that ECG abnormalities often are present during a migraine attack, and for most of these, particularly PR and corrected QT interval lengthening, these abnormalities will be absent or less prominent during pain-free intervals.