Cardiac rehabilitation is a program designed to help patients regain good health through lifestyle change after a heart attack, heart surgery or other heart problems. Patients will take part in exercise sessions and education lessons, tailored to meet their personal needs. The exercise training component of cardiac rehabilitation may be delivered as intervals of short intense sessions (also known as high intensity intervals) or the current standard care of longer but less intense sessions (moderate intense intervals). Both exercises have been shown to increase fitness levels and also prevent future risk of heart disease.

The purpose of this study is to determine the efficacy and safety of high intensity interval exercise training (HIIT) in patients who had a recent cardiac revascularization procedure or recovering from a heart attack, in comparison to current standard of moderate intensity exercise training in terms of their physical fitness and psychological well-being.

Cardiac rehabilitation is an eight week program designed to help patients regain good health through changed lifestyle after a possible heart attack, heart surgery or other heart problems. Patients will take part in exercise sessions and education lessons, tailored to meet their personal needs. The exercise training component of cardiac rehabilitation may be delivered as intervals of short intense sessions (also known as high intensity intervals) or the current standard care of longer but less intense sessions (moderate intense intervals). Both exercises have been shown to increase fitness levels and also prevent future risk of heart disease. Although there is some evidence to suggest that high intensity interval training produces better body muscles recovery and fitness during cardiac rehabilitation, many important health outcomes have not yet been determined. Such outcomes include the ability of the body to safely control blood pressure and heartbeat rate. Others include health-related quality of life and emotional well-being.

This study will explore whether there are any differences in health outcomes before and after the introduction of the intervention for patients undergoing high intensity interval exercise compared to those on moderate intensity interval exercise in terms of the recovery of the ability to control blood pressure and heartbeat rate, and also health-related quality of life and emotional well-being. In addition, patients' opinions will be sought regarding pain levels, the acceptability and the extent of enjoyment they get from each of the two types of exercise training.

For each patient, their exercise program will be designed to match their preferences and requirements. Some may prefer to work in a gym environment and so will have their program designed around this type of activity. Others may prefer to work in a group exercise circuit, with their program matched to what is available. When comparing the two types of exercise, everything will be kept the same; from the warm up and cool down, to the types of movements; the only thing that will change is the intensity of the exercise.

Before and after the eight week training program, patients will be asked to have an assessment to measure the effects that the exercise has on their body. Things like heart rate and blood pressure will be taken and they will also undergo a physical fitness test.

After the training, patients will complete questionnaires to establish their level of enjoyment of the program, how motivated they were to complete it. In addition, their quality of life and emotional well-being will be measured by completing questionnaires before and after the 8 weeks of the cardiac rehabilitation program. The investigators anticipate that a total of 46 patients will be recruited for the study over a period of 6 months. In the United Kingdom, it is believed that delivering an improved exercise training program has the potential to enhance patients' recovery from heart disease that may reduce the need for hospital services and therefore a better use of the National Health Service resources.

Inclusion Criteria:

• History of acute coronary syndromes, had a recent revascularization procedure
• History of stable heart failure or stable angina.

Exclusion Criteria:

• Unstable angina
• Systolic blood pressure of >200 mm Hg, or diastolic blood pressure >110 mm Hg (should be assessed on a case-by-case basis)
• Orthostatic blood pressure drop of >20 mm Hg with symptoms
• May have had the implantation of cardiac defibrillators (ICD)
• Synchronization devices or ventricular assist devices
• Have had a heart valve repair/replacement, a heart transplant, or grown-up congenital heart disease, critical aortic stenosis, acute systemic illness or fever, -
• Uncontrolled atrial or ventricular arrhythmias, acute pericarditis or myocarditis
• Recent embolism, thrombophlebitis, resting S-T segment depression (>2 mm), uncontrolled diabetes (should be assessed in accordance with local protocol and on a case-by-case basis)
• Severe orthopedic conditions that would prohibit exercise
• Other metabolic conditions, such as acute thyroiditis, hypokalemia or hyperkalemia, hypovolemia, severe rejection (cardiac transplant recipients), triple A >4.5 cm (if under surveillance will need confirmation from vascular surgeon as long as blood pressure remains stable)
• Tachycardia >100 beats per minute at rest, or cataracts (may commence exercise after 6 weeks)