MEDICAL SCIENCES. For the article “An advanced glycation endproduct cross-link breaker can reverse age-related increases in myocardial stiffness” by Mohammad Asif, John Egan, Sara Vasan, Garikiparthy N. Jyothirmayi, Malthi R. Masurekar, Santos Lopez, Chandra Williams, Ramon L. Torres, Dilip Wagle, Peter Ulrich, Anthony Cerami, Michael Brines, and Timothy J. Regan, which appeared in number 6, March 14, 2000, of Proc. Natl. Acad. Sci. USA (97, 2809–2813), the authors note the following correction. The name of the cross-link breaker should be 4,5-dimethyl-3-(2-oxo-2-phenylethyl)-thiazolium chloride instead of phenyl-4,5-dimethylthazolium chloride (ALT-711) as published on p. 2809, paragraph 1, line 23. We apologize for the error.