The Frank--Starling curve.

A basic property of the normal heart is that if its volume is increased, there is an increase in the strength of the contraction. The phenomenon is known as Starling's Law, and as the FrankStarling mechanism. This phenomenon is of great importance. If the heart were unable to increase its output when distended, the distension would become progressively severe. The underlying important relation in the ventri: cular muscle is that between systolic contractile force and muscle (or sarcomere) length: the lengthtension curve (Ciba Foundation Symposium, 1974). An example is shown in Fig. 1. A length of heart muscle is stimulated to contract but is not allowed to shorten. It therefore develops force isometrically. This is repeated for a range of different muscle lengths. Systolic contractile force (nor­ malized for the cross-sectional area of muscle giving stress) is plotted against length as a