What effect does nitroglycerin have on preload?

Nitroglycerin is a nitrate that primarily acts as a venous dilator. Its main mechanism involves the relaxation of smooth muscle in the venous system, which leads to dilation of the veins. This dilation results in a decrease in venous return to the heart, subsequently reducing the volume of blood returning to the heart during diastole. Since preload is defined as the initial stretching of the cardiac myocytes prior to contraction, a decrease in venous return translates to a reduction in preload.

By significantly affecting the venous capacitance vessels rather than the arteries, nitroglycerin effectively lowers the preload, leading to less volume in the heart's ventricles before they contract. This is particularly beneficial in conditions such as heart failure or angina, where reducing cardiac workload can alleviate symptoms and improve patient outcomes.