Careful thought must be given to the development of bystander pathology that could mimic worsening of heart failure. Recent trials with patients receiving amiodarone record a low rate of amiodarone pulmonary toxicity of 1.6%. Bronchoalveolar lavage in amiodarone toxicity demonstrates an absolute and relative lymphocytic alveolitis, suggesting hypersensitivity, but this finding is neither sensitive nor specific. Recently, KL-6, a mucin-like high molecular weight glycoprotein secreted by proliferating type II alveolar pneumocytes, has been identified as a potential marker of interstitial pneumonitis. A high index of suspicion combined with rapid exclusion of common confounding mimics can help in establishing the diagnosis of amiodarone lung toxicity.