Which of the following conditions results in a shifted Frank-Starling curve indicating reduced cardiac output for a given preload?

In congestive heart failure, there is a significant reduction in the heart's ability to pump effectively. This reduced contractility leads to a situation where, for a given preload (the volume of blood returning to the heart), the cardiac output is diminished. The Frank-Starling curve illustrates the relationship between stroke volume (or cardiac output) and end-diastolic volume (preload). In normal circumstances, increased preload will lead to an increase in stroke volume, due to the enhanced stretching of the myocardial fibers. However, in congestive heart failure, the heart is unable to respond appropriately to increased preload, resulting in a downward shift of the Frank-Starling curve.

This shift indicates that, at any level of preload, the heart now generates a lower output than it would under normal conditions. The heart muscle is often weakened and cannot generate enough force to eject an adequate volume of blood, thereby leading to a reduced cardiac output which is characteristic of this condition.