Calcium Imbalances produce life-threatening cardiac and neuromuscular consequences at both extremes. Hypercalcemia (>10.5 mg/dL): short QT interval, heart block and dysrhythmia, muscle weakness, altered mentation, polyuria from nephrogenic DI effect, GI hypomotility. Leading causes: hyperparathyroidism and malignancy (bone metastases, PTHrP secretion). First-line treatment: IV normal saline hydration (promotes calciuresis) — then bisphosphonates, calcitonin per orders. Hypocalcemia (<8.5 mg/dL or ionized <1.15 mmol/L): prolonged QT interval → torsades de pointes, Trousseau sign, Chvostek sign, laryngospasm, tetany, perioral numbness, seizures. Causes: hypoparathyroidism (post-thyroidectomy), pancreatitis (calcium soap formation), massive transfusion (citrate chelation), renal failure, vitamin D deficiency. Emergency nursing: calcium gluconate IV for symptomatic hypocalcemia — via central line if possible; peripheral extravasation of calcium chloride causes tissue necrosis. Cardiac monitor during infusion — bradycardia signals too-rapid administration.