Final answer:
The correct answer is C. Decreased contractility, as nifedipine, a calcium channel blocker, does not decrease the heart's contractility, which is not a therapeutic effect of nifedipine when used for angina.
Step-by-step explanation:
The question is asking which of the following is not a therapeutic effect of nifedipine when used for angina: A. Decreased preload, B. Decreased afterload, C. Decreased contractility, D. Relieve vasospasm. Nifedipine is a calcium channel blocker, specifically of the dihydropyridine class. These medications are known to have several effects on the cardiovascular system, including vasodilation which leads to decreased afterload and preload, and the relief of vasospasms. However, nifedipine is not known to decrease contractility; in fact, it tends to have a neutral effect on or may even increase contractility. Other calcium channel blockers, particularly those of the non-dihydropyridine class, are more associated with negative inotropic effects (decreased contractility). Therefore, the correct answer to the question is C. Decreased contractility.