if you suddenly feel more pain in the thighs or calves, then you should be careful. Contact a doctor immediately. Actually, clots forming in the blood may be responsible behind this pain.Actually, blood clots are formed when there is pain in the thigh or calf. In such a situation, the flow of blood in front of him starts getting obstructed and pain is experienced. However, little blood flow continues even after this. If these clots along with the blood flow reach the arteries coming out of the heart, which carry blood to the lungs, then it can obstruct the blood reaching the lungs.According to the doctor, it may take one to two days for these blood clots to reach the heart from the thigh. However, this time may vary according to the patient.