Infective endocarditis is a life-threatining infectious disease characterized by high morbidity and mortality. Leukocytes play a main role in infectious diseases. Neutrophils and lymphocytes are subgroup of leukocytes, and they are routinely measured as a part of automated complete blood count test. The neutrophil-to-lymphocyte ratio is an independent predictor of unfavorable clinical outcomes in infectious and cardiovascular diseases.