A client on a medical unit is being prepared for discharge when the monitor technician calls: the rhythm has changed. At the bedside the client feels fine and says only that their heart is "fluttering a bit." The radial pulse is 96 and irregular, but the apical rate is 128. That gap between what you hear at the apex and what you feel at the wrist is not a measurement error — it is a finding, and it tells you something specific about what the heart is doing. Atrial fibrillation is the most common sustained abnormal heart rhythm you will encounter in adult practice. Its danger is easy to underestimate because many clients tolerate it well and some do not feel it at all. The rhythm itself rarely kills anyone quickly. What it does is form clots in a quivering atrium and throw them into the circulation, and it can drop cardiac output sharply when the ventricular rate runs away. For the nurse, the whole lesson reduces to three questions asked in order. Is this client stable right now? Is...