Tumor necrosis factor antagonists (anti-TNF) are increasingly prescribed as maintenance therapy for a variety of autoimmune conditions. Therefore, frequent monitoring and awareness of side effects are of the utmost importance. Adalimumab is known to cause peripheral eosinophilia, but there are few reports of more severe adverse events. Loeffler's endocarditis is a rare and fatal disease characterized by eosinophilic infiltration of the endomyocardium leading to fibrosis and restrictive cardiomyopathy. Herein we describe a 72 year old female on adalimumab therapy for two years for rheumatoid arthritis presenting with Loeffler's endocarditis. This case represents a rare case of Loeffler's endocarditis diagnosed rapidly and without myocardial biopsy. Early intervention is crucial in the prevention of permanent fibrosis and mortality in Loeffler's endocarditis. This case demonstrates the need for close monitoring and early recognition in patients on anti-TNF therapy. Abbreviations: tumor necrosis factor (TNF), hypereosinophilic syndrome (HES).