Digoxin Lanoxin is a blood test that doctor uses to determine the level of the medication digoxin in the patient's blood. Digoxin is a medicine which contains glycosides and is used for treating heart failure and irregular heartbeats. The medicine digoxin is available in the oral form. After taking it, the patient's body absorbs it and it then travels to body's tissue especially to heart, kidney, and liver. The test is used to determine whether you are taking the accurate amount of digoxin required. Digoxin medicine monitoring is necessary because it has a very narrow safe range of intake.