The human heart is located on the left side of the body. When you sleep on your left, your entire weight is weighed down on the heart and increases the pressure on it to pump blood. Also since the left side is at a lower position, the heart is further strained by having to pump blood against gravity to the rest of the body. If you want to relieve your heart of this weight, ensure you sleep on the right side of your body. This way the heart is on the top and can easily pump blood. Sleep right, and protect your heart.