Final answer:
The three electrolytes important for myocardial rhythm/contractility are sodium, potassium, and chloride.
Step-by-step explanation:
The three electrolytes that are important for myocardial rhythm/contractility are sodium, potassium, and chloride. Sodium plays a key role in the depolarization phase of the cardiac action potential. Potassium is responsible for the repolarization phase. Chloride helps maintain the electrical balance and osmotic control of water metabolism in the body.