Mechanism of action of nifedipine is:
Nifedipine It is the first and the prototype DHP, but infrequently used now. The overriding action is arteriolar dilatation → t.p.r. decreases, BP falls. The direct depressant action on heart is significant. As described above, it does not depress SA node or A-V conduction. Nifedipine acts rapidly, due to which reflex sympathetic stimulation of heart predominates producing tachycardia, increased contractility and CO. No decrease in venous return along with lowering of afterload aids increase in CO. Coronary flow is increased. The duration of action is short (3-6 hours).
Dose: 5-20 mg BD-TDS oral.
t.p.r = total peripheral resistance.
CO = Cardiac output.
Reference: Essentials of Medical Pharmacology Eighth Edition KD  TRIPATHI  page no 595
It has a prominent smooth muscle relaxant action causes arteriolar dilation leading to fall in blood pressure
Nifedipine depresses the SA node thus decreasing myocardial excitability
Mainly depression of A-V conduction
Decrease cardiac output thus decreasing load on myocardium