If you have to miss class, you should notify your department chair or program director as soon as possible to be sure your class is covered.
If you know in advance that you will miss class, it is your obligation to arrange for a substitute, but your chair or program director may be able to help. If you have a sudden emergency, your chair or program director will work with you to make whatever accommodation the situation requires. Ad hoc re-scheduling of a missed class is not recommended since many students have tight schedules, with internships and jobs as well as other classes.
