Otto Frank (21 June 1865 – 12 November 1944) was a Grand Duchy of Hesse born medical doctor and physiologist who made contributions to cardiac physiology and cardiology.
Subsequently, from 1894 Frank worked as an assistant in Carl von Voit's Physiological Institute in Munich where he studied cardiac function using approaches derived from earlier thermodynamic analyses of skeletal muscle contraction.
This law states that "Within physiological limits, the force of contraction is directly proportional to the initial length of the muscle fiber".
Frank also undertook important work into the physiological basis of the arterial pulse waveform and may have coined the term essential hypertension in 1911.
He also worked extensively on developing accurate methods to measure blood pressure and other physiological phenomena (e.g. Frank's capsule (Frank-Kapsel), optical Spiegelsphygmograph).