Part B Which of the following can be heard with a stethoscope most easily? View Available Hint(s) Isovolumetric contraction Closing of atrioventricular valves Contraction of atria

The **closing of atrioventricular (AV) valves** can be heard most easily with a stethoscope. Here's why: 1. **Closing of Atrioventricular Valves (S1)**: - This event produces the first heart sound, commonly referred to as "lub." - It occurs at the beginning of ventricular systole when the mitral and tricuspid valves close to prevent backflow into the atria. - This sound is distinct and easily audible using a stethoscope. 2. **Isovolumetric Contraction**: - This is a phase in the cardiac cycle where the ventricles begin to contract with all heart valves closed. - Although it's a crucial part of the ventricular contraction, it doesn't produce a distinct sound that can be easily heard with a stethoscope. 3. **Contraction of Atria**: - Atrial contraction contributes to the second heart sound (S2) indirectly but doesn't produce a standalone, easily audible sound during auscultation. - Any sounds related to atrial activity are generally less prominent and not as easily distinguishable as the primary heart sounds. **Conclusion**: Among the options provided, the **closing of atrioventricular valves** is the event that can be heard most clearly and easily with a stethoscope. **Answer**: Closing of atrioventricular valves