Which electrolyte has an important influence on the muscle activity of the heart?

Potassium plays a crucial role in the electrical activity and muscle contraction of the heart. It is essential for maintaining the resting membrane potential of cardiomyocytes (heart muscle cells), which is vital for the generation and conduction of electrical impulses. A proper balance of potassium is necessary to ensure normal heart rhythm and function. Abnormal levels of potassium, whether too high (hyperkalemia) or too low (hypokalemia), can lead to significant cardiac issues, including arrhythmias or even cardiac arrest. This underlines potassium's importance in heart muscle activity.

In contrast, while sodium and calcium also have important roles in cardiac function—sodium in initiating action potentials and calcium in triggering muscle contraction—potassium is unique in its influence on repolarization and overall stability of the cardiac rhythm. Magnesium also supports cardiac function by regulating potassium and calcium levels but is less directly involved in the muscle activity of the heart compared to potassium.