How did we find out the nitroglycerin would also help people with weak hearts?

The physician William Murrell was one of the first physicians to recognize the the clinical benefits of nitroglycerin in the treatment of the heart disease known as angina pectoris, a type of chest pain caused by reduced blood flow to the heart.

Explanation:

The physician William Murrell was one of the first physicians to recognize the the clinical benefits of nitroglycerin in the treatment of the heart disease known as angina pectoris, a type of chest pain caused by reduced blood flow to the heart. He also used nitroglycerin to treat and reduce high blood pressure. He used small diluted doses of nitroglycerin to treat patients with angina pectoris. Murrell published his treatment results in the article "Nitro-glycerine as a remedy for angina pectoris," in the journal The Lancet in 1879. Thereafter, the use of nitroglycerin as treatment procedure for angina pectoris soon became generally adopted by other physicians.

Nitroglycerin is a vasodilator which is a medicine that opens blood vessels in order to improve blood flow. Nitroglycerine acts to improve blood flow to the heart by opening up or dilating the coronary arteries in the heart, thereby reducing how hard the heart has to work in pumping blood round the body. It reduces preload by  dilating veins and reduces afterload moderately by dilating arteries.

Nitroglycerin comes in two forms: quick-acting forms and long-acting forms.

The quick-acting forms include tablets or oral sprays.

Long-acting forms include pills, tablets, skin ointment, and skin patches.

the answer would be c