Etymology: Otto Frank, German physiologist, 1865-1944; Ernest H. Starling, English physiologist, 1866-1927
a mathematical expression stating that stroke volume increases with diastolic volume. The relationship is based on the principle that the force exerted by the myocardial fibers during contraction is directly proportional to their length or degree of stretch at the start of contraction. Because there are no adequate in vivo methods of measuring fiber length or diastolic volume, pulmonary artery obstructive pressure or pulmonary artery end-diastolic pressure is used as an index of diastolic volume. The relationship holds over a range of diastolic volumes. Beyond that range, the myocardial fibers are stretched past the point of maximal overlap between thick and thin filaments, and contractile force and stroke volume decrease. Also called Frank-Starling mechanism, Starling's law of the heart.