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a pharmacological agent that increases the action of the heart. Cardiac glycosides increase the force of myocardial contractions and decrease the heart rate and conduction velocity, allowing more time for the ventricles to relax and become filled with blood. These glycosides are used in the treatment of congestive heart failure, atrial flutter and fibrillation, paroxysmal atrial tachycardia, and cardiogenic shock. Toxic signs and symptoms that result from an overdose or the cumulative effect of slowly eliminated digitalis preparations include anorexia, nausea, vomiting, diarrhea, abdominal pain, headache, muscle weakness, confusion, drowsiness, irritability, visual disturbances, bradycardia or tachycardia, ectopic heartbeats, bigeminy, and a pulse deficit. Toxic effects may be attributed to an overdose or decreased growth hormone-releasing factor. Epinephrine, a potent vasopressor and cardiac stimulant, is sometimes used to restore heart rhythm in cardiac arrest but is not used in treating heart failure or cardiogenic shock. Isoproterenol hydrochloride, which is related to epinephrine, may be used in treating heart block. Inamrinone, dobutamine hydrochloride, and dopamine are used in the short-term treatment of cardiac decompensation resulting from depressed contractility.