- Digoxin loading: Only patients who demonstrate limited exercise capacity and for whom digoxin is not a risk will undergo this procedure. A medicine that makes the heart contract more strongly, digoxin is used to treat certain heart abnormalities. Patients are given doses of either digoxin or placebo (a look-alike injection with no active ingredient) at 4-hour intervals over a 24-hour period and then repeat the tilt test and the bicycle and treadmill exercise tests