Heart failure is a pump-and-volume problem that becomes dangerous when compensation can no longer protect oxygenation and perfusion. RN exam questions rarely ask the learner to recite a definition. They ask whether the nurse recognizes the cue that changes priority: rapid weight gain, orthopnea, paroxysmal nocturnal dyspnea, new crackles, falling oxygen saturation, hypotension, reduced urine output, or acute confusion. In practice, the nurse connects the mechanism to the bedside pattern. Left-sided failure raises pulmonary venous pressure and produces dyspnea, crackles, orthopnea, pink frothy sputum, and hypoxemia. Right-sided failure produces systemic venous congestion such as JVD, hepatomegaly, dependent edema, ascites, and weight gain. Many clients have both. The exam priority is not memorizing left versus right as separate lists; it is deciding whether the client is compensated, worsening, or unstable right now. Subscriber-value focus: after this lesson, the learner should be able to walk into an NCLEX-style item and answer: What cue proves decompensation? What assessment comes first? Which medication or teaching point protects the client? Which answer only delays care? On the exam, writers often pair stable-sounding options with **unstable...