Figure 199c

The effect of changing the PR interval on left ventricular sound and pusher events, as recorded by high fidelity catheter- tipped micromanmeters in anesthesided dog preparation. The M1 amplitude is markedly increased at the shorter PR intervals, while the maximal dP/dt is decreased. At the 10 msec PR interval shortens, the both M1 and notch on the dP/dt tracing occur late in systole and a plateau develop preceding the notch.