These concepts seem to suffer from an excess of experts. Each expert creates their own definition, and then argues strenuously that it is valid. For instance in 2001 James Norton identified about 30 textbooks each with a slightly different definition. In his anger and frustration, he spawned a series of his own definitions:

Preload

All of the factors that contribute to passive ventricular wall stress
(or tension) at the end of diastole

Afterload

All of the factors that contribute to total myocardial wall stress (or tension) during systolic ejection

Contractility

All of the factors that contribute to passive ventricular wall stress (or tension) at the end of diastole

These definitions are imperfect. Another article published by Carl Rothe in 2003 crticised them for being too imprecise, vaguely worded ("all of the factors") and being impossible to measure in vivo.

Rothe in his article then went on to suggest his own definitions:

Preload

Preload is the end-diastolic volume (EDV) at the beginning of systole

Afterload

Afterload is the ventricular pressure at the end of systole (ESP)

The definitions used by LITFL for afterload preload and contractility are slightly different and no less valid.

LITFL definitions

  • Preload = initial myocardial fibre length prior to contraction
  • Afterload = left ventricular wall tension required to overcome resistance to ejection (impedance to ejection of blood from the heart into the arterial circulation).
  • Contractility = the change in force generated independent of preload; synonymous with inotropy

References

Norton, James M. "Toward consistent definitions for preload and afterload."Advances in physiology education 25.1 (2001): 53-61.

ROTHE, CARL. "Toward consistent definitions for preload and afterload—revisited." Advances in physiology education 27.1 (2003): 44-45.

Noble, M. I. "Problems in the definition of contractility in terms of myocardial mechanics." European journal of cardiology 1.2 (1973): 209-216.

Solaro, R. John. "Regulation of cardiac contractility." Colloquium Series on Integrated Systems Physiology: From Molecule to Function. Vol. 3. No. 3. Morgan & Claypool Life Sciences, 2011.

Penefsky, Zia J. "The determinants of contractility in the heart." Comparative Biochemistry and Physiology Part A: Physiology 109.1 (1994): 1-22.