Which cardiovascular condition is characterized by a thickened heart muscle?

Hypertrophic cardiomyopathy is defined by a thickening of the heart muscle, particularly affecting the ventricles. This condition is often genetic and can lead to obstructive issues with blood flow as well as potentially serious arrhythmias. The thickened muscle can alter the heart's electrical pathways and impair its ability to pump blood efficiently.

Understanding the nature of hypertrophic cardiomyopathy is crucial, as it not only impacts the structure of the heart but also has significant clinical implications such as increased risk for sudden cardiac events, especially in athletes. This differentiates it sharply from other cardiovascular conditions listed in the choices. For example, aortic stenosis primarily involves narrowing of the aortic valve, atrial fibrillation is an irregular heart rhythm, and heart valve regurgitation refers to improper closure of a heart valve, leading to backflow, none of which directly lead to the thickening of the heart muscle itself.