They then close, keeping blood from flowing backward. The tricuspid valve separates the right lower heart chamber (the right ventricle) from the right upper heart chamber (right atrium). Tricuspid regurgitation is a disorder in which this valve does not close tight enough. This problem causes blood to flow backward into the right upper heart chamber (atrium) when the right lower heart chamber (ventricle) contracts. An increase in size of the right ventricle is the most common cause of this condition. The right ventricle pumps blood to the lungs where it picks up oxygen.