Nitroglycerin myocardial oxygen requirements

According to Laplace s law, a reduction in ventricular pressure and heart size results in a decrease in the myocardial wall tension that is required to develop a given intraventricular pressure and therefore decreases oxygen requirement. Since blood flow to the subendocardium occurs primarily in diastole, the reduction in left ventricular end diastolic pressure induced by nitroglycerin reduces extravascular compression around the subendocardial vessels and favors redistribution of... 

At higher concentrations, nitroglycerin also relaxes arteriolar smooth muscle, which leads to a decrease in both peripheral vascular resistance and aortic impedance to left ventricular ejection (decreased afterload). The decreased resistance to ventricular ejection may also reduce myocardial wall tension and oxygen requirements. 

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