Renal and electrolyte complications occur commonly in elderly patients with heart disease. Renal function declines with age. A seemingly normal serum creatinine level in the geriatric patient often represents a creatinine clearance of 60 ml/min or less. It is important to measure or estimate the creatinine clearance in an older patient with a borderline high or elevated serum creatinine level before administering renally excreted drugs. The Cockcroft and Gault formula is recommended for estimating the creatinine clearance in such patients. Impaired renal function can also predispose to drug-induced hyperkalemia in geriatric patients; the most common offending drugs are potassium chloride supplements, potassium-sparing diuretics, angiotensin-converting enzyme inhibitors, digoxin, and nonsteroidal anti-inflammatory drugs. Elderly patients should be evaluated for renal artery stenosis if they have worsening of previously stable hypertension, new-onset hypertension, or progressive renal impairment on angiotensin-converting enzyme inhibitors. Risk factors and management guidelines for radiocontrast nephropathy in the elderly are also discussed.