How does the heart muscle differ from the muscle in your arm?

While skeletal muscles are arranged in regular, parallel bundles, cardiac muscle connects at branching, irregular angles, called intercalated discs. Striated muscle contracts and relaxes in short, intense bursts, whereas smooth muscle sustains longer or even near-permanent contractions.

Unlike skeletal muscle tissue which you can control, cardiac muscle tissue works to keep your heart pumping through involuntary movements

answer; 60-100; beats per minute