What is the primary reason for blood backup in right-sided heart failure?

The primary reason for blood backup in right-sided heart failure is indeed the failure of the right ventricle to pump effectively. When the right ventricle is unable to contract sufficiently, it cannot adequately move blood forward into the pulmonary circulation. This leads to an accumulation of blood in the systemic venous system. As a result, pressure builds up in the veins, which can cause symptoms such as peripheral edema and congestion of the liver and spleen.

Right-sided heart failure can result from a variety of underlying causes, including increased workload from pulmonary hypertension or left-sided heart failure, but the immediate consequence of the right ventricle's failure to pump is the resultant blood backup. This is distinct from other factors that may contribute to the overall cardiovascular health but do not primarily cause the backup of blood seen in right-sided heart failure.