I'm curious as to what can cause an irregular heart beat/rhythm?

Many: If you have it ? Please ask your doctor to refer you to a cardiologist and you can ask many questions and satisfy your curiosity ok.

Many causes: Electrolyte imbalance, especially low potassium or low magnesium. Hypoxia (low oxygen). Lack of circulation (ischemia). Structural anomalies (like mitral stenosis or by-pass tract.)abnormal cardiac function (like cardiomyopathy). Infection (like myocarditis). Ph imbalance (acidosis or alkylosis). Cardiac stimulation (like nicotine, caffeine, cocaine, adrenalin). Fatigue, stress, anxiety, aging.