The heart rate is different while dancing, studying and riding a bike because the amount of blood needed for each activity is different. Blood pumps as fast as it as needed by the cells, which is why riding a bike has fast heart rate while studying has a regular heart rate.
It could be due to stress. Everyone deals with stress differently. Usually they are mad at themselves, like they have failed at supporting and that can lead to depression also.
Answer:
Blood enters the heart through two large veins, the inferior and superior vena cava, emptying oxygen-poor blood from the body into the right atrium of the heart. As the ventricle contracts, blood leaves the heart through the pulmonic valve, into the pulmonary artery and to the lungs where it is oxygenated.
