Can be normal for U. Some women with heavy periods can pass clots as well as blood during their period. It can be clots or even tissue as the lining of the uterus is "sloughing off" during your period as it is not needed for a fertilized egg. However heavy bleeding acn be a sign of another problem sucha s a bleeding disorder, thyroid disease or a uterine problem. Best to get a good history and exam to know better.