Final answer:
A patient with moderate heart failure taking a thiazide diuretic can expect improved exercise tolerance as the medication reduces blood volume by increasing urine output, which in turn reduces the workload on the heart.
Step-by-step explanation:
A patient with moderate heart failure who begins taking a thiazide diuretic can expect several outcomes. Thiazide diuretics, such as hydrochlorothiazide, work by inhibiting the Na+/Cl- symporter in the distal convoluted tubule (DCT) and collecting duct of the nephron. This results in decreased reabsorption of sodium and chloride ions, leading to increased urine output.
The most direct outcome of taking a thiazide diuretic is increased urine volume, which reduces blood volume and helps to lower blood pressure. Additionally, by decreasing the fluid overload in patients with heart failure, it can also help improve exercise tolerance by reducing the workload on the heart. While these effects can indirectly improve cardiac output and may help prevent cardiac remodeling, the primary and immediate expectation for a patient on a thiazide diuretic is an improved exercise tolerance.