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Most lecturers describing the cardiac physical examination become vague when asked to offer proof about the origin of the third heart sound. To develop a plausible explanation, researchers from Duke University performed phonocardiographic studies on seven dogs while varying their hemodynamic states with volume loading, phenylephrine, calcium infusion, and vena caval occlusion.
Before these studies, surgeons placed micromanometers into the dogs' left ventricles to measure pressure and positioned ultrasonic transducers across each left ventricle to measure ventricular diameter and oscillations. The investigators found that rapid filling of the left ventricle produced oscillations of the chamber's wall that correlated well with the S3 gallop on…