ALFRED PASIEKA / SCIENCE PHOTO LIBRARY ALFRED PASIEKA / SCIENCE PHOTO LIBRARY
Irregular heartbeat. Conceptual image of a chest X-ray overlaid with an electrocardiogram (heart monitor) trace showing extrasystole. Extrasystole is a premature contraction of the heart that momentarily breaks the normal cardiac rhythm. In this case, three contractions of the heart's ventricles (triple high peaks, right) have interrupted the normal pattern of alternating ventricular (high peaks) and atrial (low peaks) contractions. In most cases, extrasystole is sporadic and harmless. However, it can be a symptom of an underlying heart condition.
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