A pacemaker is a medical device commonly used to regulate a patient's heartbeat in cases where the heart's natural electrical impulses may be erratic or compromised. Failure of a pacemaker, or pacemaker malfunction, can be life-threatening and requires immediate action to prevent serious complications. This case report describes a 75-year-old male patient with a history of ventricular tachycardia, congestive heart failure, hypertension, and smoking who was admitted to the hospital with symptoms of palpitations, dizziness, lightheadedness, and decreased level of alertness. The patient had a single-chamber pacemaker implanted two years prior to the current admission. Upon physical examination, the patient's pacemaker had failed, and he was diagnosed with pacemaker failure. Differential diagnoses were ranked from most likely to least likely, based on the patient's history and physical examination, and included pacemaker failure, arrhythmia, myocardial infarction, and pulmonary embolism. Treatment included the replacement of the pacemaker, and the patient was discharged in stable condition.