Cardiac Muscle Action Potentials

Practice: Lidocaine is a drug that blocks voltage-gated Na+ channels. Which of the following phases of a cardiac action potential will be directly affected by the administration of lidocaine?

Practice: Verapamil is a drug that blocks voltage-gated Ca2+ channels. Which of the following phases of a cardiac action potential will be directly affected by the administration of verapamil?

Practice: Electrocardiograms (EKG) are recordings of the heart’s electrical activity made from the skin. The QRS complex of an EKG is caused by the depolarization phase of cardiac action potentials. Which of the following phases of a cardiac action potential causes the QRS complex in an EKG recording?