Define the term "heart failure."

Heart failure refers to a clinical syndrome that occurs when the heart is unable to pump blood effectively to meet the body's needs for oxygen and nutrients. This inefficiency in pumping can be due to various factors, including weakened heart muscle (systolic heart failure) or stiffening of the heart muscle (diastolic heart failure). As a result, various compensatory mechanisms may activate, leading to fluid buildup, shortness of breath, and fatigue.

In contrast, the other choices describe different medical conditions that do not encapsulate the essence of heart failure. For instance, unintentional weight loss can result from a variety of other health issues, and although it may occur in heart failure patients, it is not a defining characteristic. Meanwhile, arterial plaque buildup pertains to atherosclerosis and other cardiovascular diseases, while a sudden heart rhythm disturbance is indicative of arrhythmias, which are separate from the slow-progressing nature of heart failure. Hence, understanding heart failure as an impairment in the heart's ability to pump effectively clarifies its critical role in overall cardiovascular health.