Response to letter from Villa-Abrille et al.

As Drs. Villa-Abrille, Perez, and Cingolani correctly point out,1 the behavior whereby cardiac muscle is subjected to abruptly increased systolic load and then manifests a gradual rise in contractility has been recognized for over a century. First credited to Gleb (not Glen) von Anrep,2 its name has morphed over the decades along with the types of experiments used to generate it. The name, slow force response (SFR), has indeed been adapted by many to describe this behavior, but we feel the term is far less universal than the writers suggest, and also believe it obfuscates the mechanistic concepts behind it. What is slow—force or response? What is the response to and what …