Electrolyte imbalances can cause cardiac arrhythmias by disrupting the normal ionic balance across cardiac cell membranes. The key electrolytes involved are potassium, magnesium, and calcium. Hypokalemia causes ST depression and flattened, inverted T waves. Hyperkalemia results in peaked T waves, PR prolongation, and widened QRS complexes. Hypocalcemia and hypomagnesaemia lead to prolonged QT intervals and ST segment changes, while their hyper counterparts cause conduction delays. Diagnosis relies on identifying these characteristic ECG patterns, and treatment focuses on replacing the deficient electrolyte or removing excesses.