The green curve corresponding to a option c: blocks potassium current during repolarization only.
What is the green curve?
Potassium channels are responsible for repolarization, the process by which the cardiac cell returns to its resting state after depolarization. By blocking potassium channels, the drug in the green curve slows down repolarization, which prolongs the action potential.
Therefore, This can be useful for treating arrhythmias, such as atrial fibrillation, where the heart beats too fast or irregularly. Other drugs that block potassium channels include sotalol, amiodarone, etc. These drugs are said to be used to treat arrhythmias, but they have different side effects and levels of effectiveness.