A 34-year-old woman visited our hospital with chest pain and was diagnosed with acute myocardial infarction (AMI) on admission. Echocardiography imaging revealed the presence of complex masses in the aortic valve. As serum tumor marker CA19-9 was elevated, she was screened for malignant disease. A computed tomography (CT) scan revealed a solitary pulmonary nodule, but because the nodule was small and nonspecific, CT follow-up was considered appropriate. However, she developed hemorrhagic stroke in the short term and was subsequently diagnosed with lung adenocarcinoma. Clinicians should be on alert for the occurrence of AMI in patients with small-size lung cancer.