Why are wave summation and tetanus not possible in cardiac muscle tissue?

Cardiac muscle tissue is characterized by having long action potentials and long twitches, which play a crucial role in preventing wave summation and tetanus. During an action potential, cardiac muscle cells exhibit a prolonged refractory period due to slow calcium channels remaining open, which prevents the initiation of another action potential until the muscle has had time to relax completely. This prolonged refractory period ensures that each heartbeat is an isolated contraction, allowing the heart to pump blood effectively without the risk of prolonged contractions that could lead to inefficient pumping or even cardiac failure.

In contrast to skeletal muscle, where rapid stimulus delivery can cause wave summation leading to tetanic contractions, cardiac muscle is designed to contract and then relax fully between beats. This is essential for maintaining proper circulation and preventing arrhythmias, as continuous contractions would hamper the heart's ability to fill with blood between beats. Thus, the long duration of action potentials and twitches in cardiac cells is fundamentally important in establishing the rhythmic and coordinated contractions needed for effective cardiac function.