Frank-Starling Law

The heart adjusts its output based on how much blood returns to it - more stretch = stronger contraction.

Detailed Explanation

The Frank-Starling Law states that the stroke volume of the heart increases in response to an increase in the volume of blood filling the heart (end-diastolic volume).

Mechanism:

Increased venous return → increased preload → stretching of cardiac myocytes

Stretching optimizes actin-myosin overlap for stronger contraction

This creates a length-tension relationship

Key Points:

This is an intrinsic property of cardiac muscle (no neural input required)

Works up to a physiological limit

Failing hearts have a flattened Starling curve

Clinical Relevance:

Heart failure: decreased contractility shifts curve down and right

Volume overload: moves along the curve to the right

Diuretics reduce preload, moving back along the curve

Clinical Correlation

In heart failure with reduced ejection fraction (HFrEF), the Frank-Starling curve is flattened - the heart cannot increase output effectively with increased preload. This is why patients develop pulmonary edema with fluid overload.

Memory Trick

"The more you STRETCH, the more you can FETCH" - More stretch (preload) = More blood fetched (stroke volume)