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In patients suffering from cardiac tamponade, the inflow across the mitral valve (MV) decreases with inspiration. This is primarily due to the physiological changes that occur during the respiratory cycle.

During inspiration, negative intrathoracic pressure increases venous return to the right side of the heart. This leads to increased right ventricular filling. However, in cardiac tamponade, where there is an accumulation of fluid in the pericardial sac, the heart is unable to accommodate increased preload effectively. The distended pericardium and the constraints it imposes on the diastolic filling of the heart mean that as the right ventricle fills with blood, there is a corresponding decrease in the volume that can be accommodated by the left ventricle.

Because of this limitation in filling, the left ventricular stroke volume decreases. As a result, the volume of blood that moves across the mitral valve and into the left ventricle during diastole subsequently decreases with each respiratory cycle, leading to a net reduction in mitral inflow during inspiration. This decrease is a key indicator of the hemodynamic consequences of cardiac tamponade, reflecting the impaired diastolic function of the heart.