What effect does respiration have on heart sounds?

Respiration influences heart sounds primarily through changes in intrathoracic pressure, which affects venous return to the heart. During inspiration, the negative pressure increases venous return, often resulting in a slight increase in heart sounds due to enhanced blood flow. Conversely, during expiration, venous return decreases, which can lead to a reduction in the intensity of heart sounds. This respiratory variation is particularly notable in conditions like pericardial effusion, where heart sounds may become muffled and vary with respiration.