"In his postdoctoral work (Habilitationsschrift) Frank investigated the isometric and isotonic contractile behaviour of the heart and it is this work that he is best known for. Frank's work on this topic preceded that of Ernest Starling, but both are usually credited with providing the foundations of what is termed the Frank–Starling law of the heart. This law states that "Within physiological limits, the force of contraction is directly proportional to the initial length of the muscle fiber" (Wikipedia article on Otto Frank, accessed 4-2020).

Translated into English with commentary by Carlton B. Chapman & Eugene Wasserman, "Translators note in relation to a Special Article 'On the Dynamics of Cardiac Muscle' by Otto Frank," American Heart Journal , 58 (1959) 282-317.

"The First Mathematical Description of the Pressure-Volume Diagram 

"Not until 60 years after 1899 Otto Frank's mathematical formulation of the volume-pressure diagram and his concept of the mechanism of the cardiac work of the left ventricle cardio-physiologists began to rediscover Frank's work systematically. Frank's scientific development proves his constant commitment to and deep interest in understanding and analysing physiological problems mathematically. Consequently Frank worked on the quality and theory of physiological instruments and the problems of measurement, to calculate the influence in experimental research of the cardio-vascular system. Besides Frank's publications on different types of manometers his theory of "Windkessel" function as a model of the mechanics of the left ventricle and the different energies of the cardiac work are of importance even today, although we know only few details of his life as a pupil of Carl Ludwig and Carl von Voit and as a professor of physiology in Giessen and Munich." (B. Lohff, https://pubmed.ncbi.nlm.nih.gov/10705804/) Translated into English by K. Sagawa K, R.K. Lie, J. Schaefer, J Mol Cell Cardiol 22 (1990) 253-277.

Frank obtained the first perfect pulse curves with special manometers, the so-called “Frank capsules”.