Abnormally rapid heartbeat, greater than 100 beats per minute. Tachycardia can result from poisoning, medications, certain illnesses, and during states of anxiety or excitement. A rapid heartbeat is normal for the very young or during the physical exercise of normal adults. While not a diagnostic feature in itself, PDD examiners pay attention to heart rate during evaluation of the polygraphs as it may signal pharmaceutical countermeasures or atypical levels of stress.