Through venous vasodilation, nitrates decrease the return of blood to the heart and reduce preload, ventricular size and systolic wall tension. The composite effect on the demand side is to decrease the hearts oxygen consumption. In experimental studies, nitrates have been shown to augment blood flow to ischemic areas of myocardium through vasodilation of collateral blood vessels. Nitrates therefore affect both the myocardial oxygen supply and demand through vasodilation. It was previously believed that increased blood flow may be the primary therapeutic effect of nitrates in coronary artery disease. However, new evidence implies that the principal action may be different in different patients: patients with significant vasoconstrictive coronary artery disease may benefit from the vasodilatory effect of nitrates and augmentation of blood delivery, whereas patients with constant threshold angina may benefit from reduction in oxygen consumption as the principal favorable effect of nitrates. asthma inhalers
The balance of oxygen supply and demand in the subendocardium is favorably affected by nitrates. By reducing left ventricular end-diastolic pressure, nitrates decrease the systolic wall tension and the extravascular forces impeding blood flow to the subendocardium.