REN and heart failure: Previous studies have found that testosterone replacement therapy is likely beneficial for patients with chronic kidney disease.25,26 However, testosterone supplementation has been associated with increased blood pressure, sodium and water retention, and activation of vasoconstrictor systems in the kidney, such as the renin-angiotensin system and endothelin, which can compromise renal function.27 Given our results, careful monitoring and consideration of the patient’s renal status are essential when initiating testosterone therapy in heart failure patients.