NLN NEX Science Practice Test 2026 – The Complete Guide to Mastering Your Exam!

The heart is driven by a muscle designed to pump continuously without conscious effort. That muscle is cardiac muscle, which forms the walls of the heart and contracts in a coordinated, rhythmic way. It is involuntary, meaning you don’t consciously control each heartbeat—the autonomic nervous system and the heart’s own conduction system handle the rhythm. Cardiac muscle is also striated like skeletal muscle, but its activity isn’t under voluntary control. In contrast, smooth muscle (non-striated, in hollow organs) and skeletal muscle (voluntary, attached to bones) don’t fit the combination of being in the heart and being involuntary. So the muscle type present in the heart and involuntary is cardiac muscle.