The patient with paresthesias who complains of heart palpitations is exhibiting signs of symptomatic hyperkalemia, which places the patient at risk for a fatal arrhythmia if not diagnosed quickly. The patient who complains of tachycardia and dizziness upon standing likely has an orthostatic hypotension/tachycardia; this patient’s condition is not life-threatening. The patient with a radial pulse of 215 bpm while calm likely has a supraventricular tachycardia; however, the fact that the radial pulse is palpable for counting indicates the patient’s heart is perfusing the body despite the increased rate. This patient can wait until after the patient with symptomatic hyperkalemia. The patient receiving digoxin, which is prescribed for atrial fibrillation, who calls out to report sudden dyspnea is exhibiting signs of a pulmonary embolism. While this patient requires prompt intervention, a 12-lead EKG is not the most important test for the patient.