In total anomalous pulmonary venous return (TAPVR), the pulmonary veins incorrectly send blood to the heart's upper right chamber. That chamber is called the right atrium. As a result, oxygen-rich blood mixes with oxygen-poor blood, as shown in purple. In a typical heart, shown on the left, oxygen-rich blood flows from the pulmonary veins to the upper left chamber, also called the left atrium.