Excess K⁺ in cardiac tissue causes

A) an increased heart rate.
B) a rapid repolarization of cardiac cells.
C) a decrease in the frequency of action potentials in the conduction system.
D) an increase in stroke volume.
E) an increase in the frequency of action potentials.

Excess K⁺ in cardiac tissue would likely lead to hyperpolarization of cardiac cells, making them less excitable and thus decreasing the frequency of action potentials in the conduction system. This would slow down the heart rate rather than increasing it, affecting the rhythm rather than directly increasing stroke volume or causing rapid repolarization.