Patent infringement requires that every element and limitation in a correctly construed claim is embodied in the accused system either literally or, if embodied by an equivalent, in compliance with the rules of equivalency as set forth in Festo Corp. v. SMC Corp., 535 U.S. 722 (2002) and Warner-Jenkinson Co. v. Hilton Davis Chemical Co., 520 U.S. 17 (1997) and implementing rulings.

The defendant, Zoll Medical, made a CPU-based device designed to interface with a personal computer.

The elements of the '685 patent claims on which the district court relied are "general purpose computer" and "interactive display input." The district court found that neither of these elements is present in the Zoll system, and on this basis granted summary judgment of non-infringement.

[T]he term "general purpose computer" was added to Hutchins' claims during prosecution in order to distinguish the '685 invention from prior art that showed similar devices with dedicated microprocessor units. This produced an estoppel against reading the term "general purpose computer" to include a dedicated microprocessor such as a RISC, for the claims had been amended in response to the PTO rejection, thereby estopping recovery of the same subject matter that the claims had been amended to exclude. See Alloc v. Int’l Trade Comm’n, 342 F.3d 1361, 1371-72 (Fed. Cir. 2003) (statements made during prosecution surrendering subject matter binding on later interpretation of the claims); see also Festo, 535 U.S. at 725 (estoppel arises upon amendment to "surrender the particular equivalent in question"); Bayer AG v. Elan Pharm. Research Corp., 212 F.3d 1241, 1252 (Fed. Cir. 2000) (an aspect expressly disavowed during prosecution of the patent cannot be reached under the doctrine of equivalents).

The Zoll device requires no input from the rescuer, who places electrical contacts as directed by the device; the device then monitors the victim's heart and determines whether CPR or an electric shock is necessary. The district court observed that although the Zoll system analyzes characteristics such as heart rhythm, it does not provide for interactive input by the rescuer.

Hutchins also dreamt up a copyright infringement suit, that Zoll had copied his source code, that was less than dreamy.