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.
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 systole is not altered in length, but the diastole is very much prolonged, and since this is the period not only of cardiac rest but also of cardiac "feeding" - the coronary vessels being compressed and occluded during systole - the result is greatly to benefit the nutrition of the cardiac muscle.
The individual muscle-fibres contract and expand more perfectly, and thus the diastole and systole of the heart are rendered more complete, the pulse is slowed, and the blood-pressure is raised.
The blood-pressure synchronously falls, and the heart is arrested in 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.