Note: The diagram at right (and in Fig. 2.05) shows what happens in the first few cardiac cycles after contractility is abruptly increased. It reflects more accurately the real world than the previous two figures (A & B). Clearly, afterload and preload are altered, because they are all mechanically inter-related. Increased strength of contraction at first increases ventricular emptying, ie. increases stroke volume and ejection fraction. The point at which the aortic valve closes moves down the isovolumic pressure line. This increases blood volume in the aorta and the arterial tree, increasing afterload. This later tends to readjust upward, the point at which the aortic valve closes. Increased movement of blood to the arteries, empties the veins and decreases preload. This tends to move to the left the point at which the mitral valve closes.
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