What is the primary effect of nitroglycerin in cardiac patients?

Nitroglycerin is primarily used in cardiac patients for its ability to dilate blood vessels, which leads to improved blood flow and a reduction in cardiac workload. The mechanism of action involves the relaxation of smooth muscle in the blood vessel walls, resulting in vasodilation. This process decreases both preload and afterload, which can relieve the heart's demand for oxygen.

When nitroglycerin is administered, it primarily affects the venous system, allowing more blood to pool in the peripheral veins and decreasing the volume returning to the heart. This reduces the workload on the heart itself during moments of stress or ischemia, such as in cases of angina or heart failure. Additionally, the dilation of arteries can help improve oxygen delivery to myocardial tissues, further alleviating pain and discomfort associated with cardiac conditions.

The other options do not accurately represent the primary effects of nitroglycerin. Increasing heart rate, constricting blood vessels, or stabilizing heart rhythm are not direct effects of nitroglycerin's action and do not capture its vasodilatory properties, which are key to its therapeutic use in treating cardiac patients.