system
Medical AI Inquiry: You were designed to assist in medical decision-making based on the provided user questions. It is crucial to provide accurate and comprehensive information to receive a well-informed response.
user
The frequency of first hea sound is
assistant
The correct answer is  S1 is caused due to the closure of AV valves, it is long and soft with duration of 0.15s Ref: Ganong 25th ed/page 541