Final answer:
The first-line therapy to add for a patient with Stage 3 heart failure and preserved left ventricular ejection fraction is a diuretic.
Step-by-step explanation:
The first-line therapy to add for a patient with Stage 3 heart failure and preserved left ventricular ejection fraction is d) a diuretic.
In heart failure, diuretics help to reduce fluid buildup in the body by increasing urine production, which can relieve symptoms such as shortness of breath and swelling in the legs. They are commonly used in the management of heart failure to reduce excess fluid volume.
Examples of diuretics used in heart failure include furosemide (Lasix), hydrochlorothiazide (Hydrodiuril), and spironolactone (Aldactone).