Overview Cardiovascular disease (CVD) is the greatest cause of morbidity and premature mortality in western society and is an umbrella term for a number of disorders, including coronary artery disease, heart failure, valvular disease, peripheral vascular disease and stroke. The UK has seen a reduction in the mortality of CVD, mainly due to the advancement of medical care and surgical interventions, but also as a result of alteration in lifestyle risk factors of patients following diagnosis through cardiac rehabilitation activities. This chapter will focus on the role of physical activity in the rehabilitation of those diagnosed with a cardiac condition. The Cardiovascular System The heart consists of four chambers, the 'upper' right and left atrium and the 'lower' right and left ventricles. Valves between the upper and lower chambers ensure the one directional flow of blood. Both atrium contract at approximately the same time, as do both ventricles, ejecting blood out of the heart ensuring effective blood flow to the pulmonary (right side of the heart) and systemic circulation (left side of the heart). The heart muscle, the myocardium, receives its supply of blood and nutrients via the coronary arteries, which form part of the coronary circulation. The coronary circulation emerges at the root of the aorta, distributing blood and oxygen to the myocardium, with deoxygenated blood returned to the right atrium via coronary veins. The two main coronary arteries