Digoxin is a cardiac glycoside used to treat congestive heart failure and abnormal heart rhythms, namely atrial fibrillation and atrial flutter, which cannot be controlled by other medications. The main cardiac effects of Digoxin are: A decrease of conduction of electrical impulses through the AV node, making it a commonly used antiarrhythmic agent in controlling heart rate, and an increase of force of contraction via inhibition of the NA+/K+ ATPase pump. Digoxin, therefore, strengthens the contractions of the heart and helps it to pump blood more efficiently, and helps control the heart rate and abnormal heart rhythms known as arrhythmias. This test is useful in monitoring the levels of Digoxin in blood because it has a narrow safety range. If the levels are too LOW, symptoms may recur, and if the levels are too HIGH, toxicity may occur with possible side effects such as dizziness, blurred vision, vomiting, diarrhea, and difficulty breathing.