Which of the following is a sign of congestive heart failure?

Rapid breathing, or tachypnea, is a common sign of congestive heart failure (CHF). In CHF, the heart is unable to pump blood effectively, which can lead to fluid buildup in the lungs and result in pulmonary congestion. This fluid accumulation stimulates the respiratory system, causing a sensation of breathlessness and prompting an increase in breathing rate as the body attempts to improve oxygenation and cope with the impaired gas exchange.

In contrast, severe dehydration typically presents with symptoms such as dryness of the mouth, decreased urine output, and possibly confusion, which are not directly indicative of heart function. Cyanosis, while it can occur in CHF due to impaired oxygenation, is more typically associated with severe respiratory hardship or other conditions. Acute chest pain can arise from various issues, such as myocardial infarction or pulmonary embolism, but it is not a direct sign of congestive heart failure. Thus, rapid breathing is the most characteristic sign among the options provided, linking directly to the physiological effects of heart failure.