What is defined as the lack of normal, rhythmic beating of the heart?

The correct answer is arrhythmia, which refers to any irregularity or abnormality in the heartbeat, including the absence of a normal, rhythmic beating pattern. Arrhythmias can manifest in various forms, including tachycardia (a fast heartbeat), bradycardia (a slow heartbeat), or a complete lack of rhythmic contractions, highlighting its broad definition.

Other terms in the choices have specific meanings that do not encompass the general definition provided. Bradycardia specifically indicates a slower than normal heart rate but does not address the rhythmic aspect. Palpitations refer to the sensation of feeling the heart beating irregularly or too strongly, which is more of a subjective experience rather than a clinical definition of the rhythm itself. Cardiomyopathy involves disease of the heart muscle, which can lead to arrhythmias but does not define the beat's rhythmic nature itself. Thus, arrhythmia is the most accurate term used to describe the lack of normal, rhythmic beating of the heart.