This document discusses various cardiac rhythms categorized by heart rate and QRS complex characteristics. It distinguishes between tachycardia and bradycardia, and then provides further classifications for each based on factors like QRS width, regularity, presence of P waves, and underlying rhythm. Common rhythms mentioned include sinus tachycardia, atrial flutter, junctional tachycardia, atrial fibrillation, sinus bradycardia, heart block, and slow atrial fibrillation.