Panic attacks, along with the sense of impending doom, walls closing in, shortness of breath, and chest pressure, also include palpitations, which is due to the excessive sympathetic response (
flight or fight) due to adrenaline
in the blood. The palpitations can be just due to the
heart beating stronger from the increased stimulation, or can actually be abnormal beats caused by the adrenaline over stimulating heart cells which then activate early or abnormally.