Inappropriate sinus tachycardia (IST), a syndrome characterized by unexpectedly fast sinus rates at rest, with minimal physical activity, or both, is manifest by a spectrum of symptoms including palpitations, weakness, fatigue, dizziness, or near syncope. Acceleration in rate with minimal exercise is excessive and heart rate recovery is prolonged. Sinus tachycardia, even if excessively fast, generally is a transient and reversible condition with an explainable cause and a rate appropriate for the circumstance (caffeine ingestion, anxiety, deconditioning, and so on.) (1). IST is a more long-standing problem that is not as easy to explain. Herein, we review IST, explore its mechanisms, and review management strategies.