We herein report an autopsied case of a patient with adenocarcinoma of the lungs who developed nonbacterial thrombotic endocarditis (NBTE) that caused acute heart failure (AHF) due to acute aortic stenosis (AS). A 37-year-old man was admitted to our hospital due to chest pain and fever. He was diagnosed as having Stage IV lung cancer. Following the administration of chemotherapy, the patient presented with acute onset of dyspnea. He was diagnosed with having AHF based on his clinical course and physical findings, and ultimately he died without responding to treatment. The autopsy revealed that NBTE caused acute AS leading to AHF.