The initial evaluation is mainly directed at diagnosing associated conditions (eg, valvular heart disease, hypertension, evidence of heart failure). The cardiac examination during atrial fibrillation will show an irregularly irregular rhythm, variability of the first heart sound, and augmentation of a systolic murmur after long pauses. The initial evaluation of new-onset atrial fibrillation also includes a detailed history focusing on possible precipitating factors as well as the presence of organic cardiac disease. As such, the initial evaluation includes, at a minimum, a careful physical examination, 12-lead electrocardiogram (ECG), chest radiograph, echocardiogram, and tests of thyroid function. Further testing will depend on various aspects of the history or physical examination. Ambulatory ECG monitoring may be helpful in diagnosing the patient with paroxysmal atrial fibrillation. For example, if atrial fibrillation is usually precipitated by exercise, then an exercise treadmill test is appropriate. In the patient with frequent episodes of paroxysmal atrial fibrillation, a 24- to 48-hour ambulatory ECG recording may discern whether atrial fibrillation was triggered by another arrhythmia, such as a premature atrial complex alone, or whether the fibrillation was preceded by an episode of supraventricular tachycardia. In addition, patients with vagally mediated fibrillation will typically have episodes either after heavy meals or during sleep. These clues may help identify those patients who may respond to specific approaches (see later section, Treatment).