Preload leads to

The force of contraction of cardiac muscle depends on its preloading and its after loading. The initial phase of contraction is isometric; the elastic component in series with the contractile element is stretched and the tension increases until it is sufficient to lift the load. The tension at which load is lifted is the afterload. The muscle then contracts isotonically. In vivo preload is the degree to which myocardium is stretched before it contracts.Ref: Ganong&;s Review of medical physiology, 24th edition.Pg no. 547