Which electrolyte disturbance can significantly affect cardiac function?

Potassium imbalance plays a crucial role in cardiac function due to its direct impact on the heart's electrical activity. Potassium is essential for the generation and conduction of electrical impulses within the heart. Abnormal potassium levels, whether hyperkalemia (elevated potassium) or hypokalemia (lowered potassium), can lead to significant arrhythmias, altered heart rates, and even cardiac arrest.

In hyperkalemia, the elevated potassium levels can result in a decreased resting membrane potential, making cardiac myocytes more depolarized and leading to disturbances in the heart rhythm. Conversely, hypokalemia can result in increased myocardial excitability and potentially dangerous rhythms.

While sodium, phosphate, and chloride imbalances can have various physiological effects, their direct impact on cardiac electrical activity is not as pronounced as that of potassium. Thus, potassium imbalance stands out as particularly critical for maintaining normal cardiac function, making it the correct answer in this context.