The drug is contra-indicated in all cases where the heart is already beating too slowly; in aortic incompetence - where the prolongation of diastole increases the amount of the blood that regurgitates through the incompetent valve; in chronic Bright's disease and in fatty degeneration of the heart - since nothing can cause fat to become contractile.
The blood-pressure synchronously falls, and the heart is arrested in diastole.
The " dup " sound is caused by the closing of the aortic and pulmonary valves at the beginning of ventricular diastole.
Diastolic blood pressure-Diastole is the period in which the left ventricle relaxes so it can refill with blood; diastolic pressure is therefore measured during diastole.
Later in its action, the drug depresses the intra-cardiac motor ganglia, causing prolongation of diastole and finally arrest of the heart in dilatation.