Which of the following is a sign of left-sided heart failure?

Tachycardia is indeed a common sign of left-sided heart failure. In this condition, the heart's ability to pump blood effectively is impaired, leading to a reduced output of blood. As a compensatory mechanism, the body increases heart rate to maintain adequate circulation and oxygen delivery to tissues. This elevated heart rate is an indicator that the body is trying to adjust to the heart's decreased efficiency.

Other symptoms associated with left-sided heart failure may include shortness of breath (dyspnea), fatigue, and pulmonary congestion, which arise from the buildup of fluid in the lungs due to the heart's inability to manage blood volume effectively. This context helps to clarify why tachycardia is a relevant symptom in this situation, demonstrating the heart's effort to compensate for its failing function.