What is the timing and, of course, most important, what is the significance of the movement at the lower left sternal edge? Well, the timing to begin with is very similar to the timing of the movement at the upper left sternal edge. So, we'll use our cotton swab again and compare those movements, upper left, lower left. Everyone observe together. [cut-away]

And what did we learn from evaluating the impulse at the lower left sternal edge? Well, to begin with, more simple anatomy, the right ventricle occupies the area at the mid-lower left sternal edge, so by all odds, this is an enlarged right ventricle. But, by timing the impulse at the lower left sternal edge, comparing to that at the upper, we learned that that impulse was early in systole, it was non-sustained, so we have also learned the pathophysiology of that enlargement. The early timing, the hyperdynamic nature tells us, by all odds, that the genesis of that enlargement is volume, or preload. In contrast, when a right ventricle is "enlarged" due to hypertrophy, the impulse lasts much longer in systole and it is much more sustained.