The mitral valve is located in the heart. It lies between the left atrium and the left ventricle. The mitral valve opens to increased pressure as the left atrium fills with blood. Blood flows through into the left ventricle as the heart expands (diastole). It then closes as the heart contracts (systole) and forces blood into the aorta. This process is vital to the heart's function. Sometimes the mitral valve doesn't close properly; this is known as mitral valve prolapse. This may cause blood to leak the wrong way, known as regurgitation, which leads to shortness of breath, palpitations, and chest pain. However, in many cases, there is still a tight enough seal to prevent regurgitation, so many people do not know that they have mitral valve prolapse. Occasionally, mitral valve prolapse may lead to infective endocarditis. This is a form of infection that inflames the heart, and it is treated with antibiotics.