Tachycardia

Your heart is racing. Without warning, without any apparent reason. You're sitting on the sofa, lying in bed, or walking through the supermarket — and suddenly your heart is hammering at one hundred and thirty, one hundred and sixty beats per minute. Your chest tightens, your breath becomes shallow, and a feeling spreads through you as though your body is preparing for a flight that has no cause.

Medically, tachycardia is an elevated heart rate above one hundred beats per minute. There are cardiac causes, hormonal causes, medication-related causes. But there are also cases — and they are more common than most people think — where no examination yields a finding. The heart races, and no one can say why.