Making the world better, one answer at a time. Causes of extrasystole include alcohol, ischemia, hypoxia, and myocarditis. Extrasystole is defined as a premature beat in the heart that causes momentary arrhythmia. Causes of extrasystole include alcohol, ischemia, hypoxia, and myocarditis. Extrasystole is defined as a premature beat in the heart that causes momentary arrhythmia.