The Effect of Sublingual Nitroglycerin on Absolute Coronary Blood Flow

The goal of this clinical trial is to investigate the effect of sublingual nitroglycerin on absolute coronary blood flow in adult patients undergoing coronary angiography. The main questions it aims to answer are: * Does sublingual nitroglycerin change absolute coronary blood flow compared to placebo? * What is the effect of sublingual nitroglycerin on important cardioavascular parameters such as coronary pressure and resistance? Researchers will compare the sublingual nitroglycerin group to the placebo group to see if nitroglycerin leads to significant changes in coronary blood flow and microvascular function. Participants will: * Receive either sublingual nitroglycerin or a placebo during coronary angiography. * Undergo coronary blood flow measurements before and after the intervention using standardized assessment techniques.