Increases in intracellular calcium enhance myocardial contraction and result in a positive inotropic effect.
Digoxin causes an increase in vagal tone which decreases the rate of SA node depolarization.
Acute Overdose Digoxin naive patients, with no preexisting cardiac abnormalities, are relatively resistant to developing ventricular arrhythmias. Most often seen are heart block with or without supraventricular arrhythmias. Other effects include vomiting, bradycardia, and hyperkalemia. These patients may present with a variety of types of arrhythmias, most being ventricular. Other effects seen include nausea, vomiting, visual disturbances and altered mental status.