Which of the following is a common type of arrhythmia?

Atrial fibrillation is a common type of arrhythmia characterized by an irregular and often rapid heart rate, which can lead to various cardiovascular complications. It occurs due to chaotic electrical signals in the atria of the heart, causing the heart's upper chambers (the atria) to quiver instead of contracting effectively. This irregularity can disrupt the normal blood flow, increasing the risk of stroke and other heart-related issues.

In contrast, the other options listed are not types of arrhythmias. Myocardial infarction, or heart attack, is a result of interrupted blood flow to the heart, leading to tissue damage. Acute pancreatitis is an inflammatory condition of the pancreas, and pneumonia refers to a lung infection. While these conditions can significantly impact heart function and may lead to arrhythmias as a secondary effect, they are not arrhythmias themselves. Therefore, atrial fibrillation stands out as the sole common type of arrhythmia among the provided choices.