Valvular heart disease is a common cardiac condition that occurs when heart valves are damaged or diseased. Affected valves can be stenotic (narrow) or regurgitant (leaky) leading to inefficient blood flow from the heart. This chapter focuses on the left-sided heart valves—aortic and mitral valves—that are commonly affected. Stenotic valves, like in aortic and mitral stenosis, prevent easy flow of blood out of the heart and can lead to symptoms like chest pain, dizziness, and heart failure. Over time, to compensate for increased heart pressures, these conditions can lead to structural changes in the heart including atrial enlargement, which also increases the risk of atrial fibrillation. Regurgitant valves, like aortic and mitral regurgitation, result in backflow of blood due to incomplete valve closure and can lead to heart failure. The degree of stenosis or regurgitation, along with symptom severity, helps guide treatment, which include medication, minimally invasive procedures, or surgery.