Blood cultures in patients with infective endocarditis for at least 3 weeks. 1. For patients with acute infective endocarditis: 10-20 ml of venous blood should be collected at 1 hour intervals within 3 hours of admission, with a total of 3 blood collections followed by aerobic and anaerobic cultures for at least 3 weeks. 2. For patients with untreated subacute infective endocarditis: blood should be collected at 1-hour intervals on day 1 for a total of 3 times, and if no bacterial growth is detected on the following day, antibiotic therapy can be given after repeating the blood collection 3 times. However, blood cultures may be negative in endocarditis caused by Candida, Pathogen Q fever, and Aspergillus infections. In case of unexplained fever and abnormal ultrasound results, it is recommended to consult a doctor to clarify the cause of the disease and provide targeted management or treatment.