The main pharmacological effects of digoxin are on the heart . Extracardiac effects are responsible for some of the therapeutic and many of the adverse effects (see above). It exerts a mechanical effect as it increases myocardial contractility; however, the duration of the contractile response is only slightly increased. High ventricular rate leads to insufficient diastolic filling time. By slowing down the conduction in the AV node and increasing its refractory period, digoxin can reduce the ventricular rate. The arrhythmia itself is not affected, but the pumping function of the heart improves, owing to improved filling.