A 76-year-old woman underwent an ECG examination in her family doctor's office which showed atrial fibrillation with a controlled ventricular rate of 66 beats per minute, as evidenced by the lack of P waves and presence of fibrillatory waves, irregularly irregular rhythm, and normal QRS axis, duration, and absence of signs of right or left ventricular hypertrophy, bundle branch blocks, myocardial infarction, or other abnormalities.