A neuroendocrine carcinoma of the lung associated with bradycardia and episodic cardiac asystole is reported. Cardiac dysfunction may have been caused by a hormonal factor produced by a carcinoma developing in the pulmonary neuroepithelial bodies because the bradycardia and periods of asystole disappeared after pneumonectomy, only to return months later when pleural metastatic tumor developed. No neoplastic involvement of the heart was present. Implications of a cholinesterase isoenzyme involvement in the cardiac dysfunction are discussed.