Hi, Menstruation is the process of shedding of the uterine lining along with the blood in case of absence of fertilization. Blood clots found during the cycle is often normal. When there is associated symptoms with clots, it should be evaluated. Blood clots during the menstrual cycle contains blood red cells, tissues forming the lining of the uterus and the proteins. Protein helps to coagulate the blood and preventing the excessive blood loss from the uterine blood vessels. These clots are formed when there is more space to collect the blood for certain amount of time during when there is coagulation occurs and the clot forms. Certain conditions can cause heavy menstrual blood flow associated with painful cycles. Uterine polyps, fibroids, adenomyosis, endometriosis, enlarged uterus, hormonal imbalance are some of the cause for heavy painful menstrual flow along with blood clots. If the clots are associated with severe pain and heavy blood loss, consult a gynecologist for further evaluation. Take care. Hope I have answered your question. Let me know if I can assist you further. Regards, Dr. Pradeepraj, General & Family Physician