If you're starting a self guided fitness program you should complete a pre-participation assessment, like the PAR-Q, in order to identify if you have an increased risk and to determine if a medical evaluation is warranted. From the ACSM's Guidelines for Exercise Testing and Prescription

Physical Activity Readiness Questionnaire (PAR-Q)

Please answer each question honestly, use common sense as your guide.

1. Has your doctor ever said that you have a heart condition and that you should only do physical activity recommended by a doctor.
2. Do you feel pain in your chest when you do physical activity?
3. In the past month, have you had chest pain when you were not doing physical activity?
4. Do you lose your balance because of dizziness or do you ever lose consciousness.
5. Do you have bone or joint problem (for example, back, knee or hip) that could be made worse by a change in your physical activity?
6. Is your doctor currently prescribing drugs (for example, water pills) for your blood pressure or heart condition? Do you have high blood pressure?
7. Do you know of any other reason why you should not do physical activity?

If you answered YES to one of the questions talk with your doctor by phone or in person BEFORE you start becoming much more physically active or BEFORE you have a fitness appraisal or start working with FitTec. Tell your doctor about the PAR-Q and which questions you answered YES.
You may be able to do any activity you want as long as you start slowly and build up gradually. Or, you may need to restrict your activities to those which are safe for you. Talk with your doctor about the kinds of activities you wish to participate in and follow his/her advice. Find out which community programs are safe and helpful for you.

If you answered NO honestly to all PAR-Q questions, you can be reasonably sure that you can start becoming much more physically active-begin slowly and build up gradually. This is the safest and easiest way to go. You should take part in a fitness appraisal - this is an excellent way to determine your basic fitness so that you can plan the best way for you to live actively. It is also highly recommended that you have your blood pressure evaluated. If your reading is over 140/90, talk with your doctor before you start becoming much more physically active. PAR-Q: The Canadian Society for Exercise Physiology

After completing the PAR-Q find if you have any coronary artery disease risk factors and major signs or symptoms of disease. This would help you identify further your risk stratification.
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Coronary Artery Disease Risk Factors

Positive risk factors
1. Family history
Myocardial infarction, coronary revascularization, or sudden death before 55 years of age in father or other male first degree relative, or before 65 years of age in mother or other female first-degree relative.

2. Cigarette smoking
Current cigarette smoker or those who quit within the previous 6 months

3. Hypertension
Systolic blood pressure >140 mm Hg or diastolic >90 mm Hg, confirmed by measurements on at least two separate occasions, or on antihypertensive medication.

Those with hypertension may need additional tests and clearance before participating in an exercise program. Consult with a physician.

4. Dyslipidemia
Low-density lipoprotein (LDL) cholesterol >130 mg/dL (3.4 mmol/L or high-density lipoprotein (HDL) cholesterol <40 mg/dL (1.03 mmol/L), or on lipid-lowering medication. If total serum cholesterol is all that is available use >200 mg/dL (5.2 mmol/L) rather than low-density lipoprotein (LDL) >130 mg/dL.

5. Impaired fasting glucose
Fasting blood glucose >100 mg/dL (5.6 mmol/L) confirmed by measurements on at least two separate occasion

6. Obesity
Body mass index > 30 kg/m-2 or Waist girth >102 cm for men and >88 cm for women or Waist/hip ratio: >0.95 for men and >0.86 for women

7. Sedentary lifestyle
Persons not participating in a regular exercise program or not meeting the minimal physical activity recommendations> from the U.S. Surgeon General's Report.

Depression may be a positive risk factor as well.

Negative risk factors
High serum HDL cholesterol > 60 mg/dl (1.6 mmol/L)

Special consideration is suggested to those with hypertension. The ACSM points out that the Joint National Committee on the Prevention, Detection, and Treatment of High Blood Pressure recommends a thorough medical history, physical examination, laboratory tests, and other diagnostic procedures when exercise screening those with hypertension.

Major Signs or Symptoms of Disease

Pain, discomfort (or other anginal equivalent) in the chest, neck, jaw. arms, or other areas that may result from ischemia

Shortness of breath at rest or with mild exertion
Dyspnea-abnormally, uncomfortable awareness of breathing

Orthopnea-dyspnea at rest that is relieved by sitting up or paroxysmal nocturnal dyspnea (dyspnea occurring 2 to 5 hours after onset of sleep)

Dizziness or syncope (loss of consciousness)

Ankle edema

Palpitations (unpleasant awareness of forceful or rapid beating heart) or tachycardia (racing heart rate)

Intermittent claudication-pain that occurs in a muscle due to inadequate blood flow during exercise. Feels like a cramp that goes away after stopping.

Known heart murmur

Unusual fatigue or shortness of breath with usual activities-usually benign but might be a signal of a change.

The ACSM Risk Stratification
Low risk
Men <45 years of age and women <55 years of age who are asymptomatic and meet no more than one risk factor
Moderate risk
Men >45 years and women >55 years or those who meet the threshold for two or more risk factors
High risk
individuals with one or more signs and symptoms or known cardiovascular, pulmonary, or metabolic disease

The ACSM suggest that moderate to high risk individuals receive medical clearance with a stress test before starting a vigorous exercise program.

Moderate to high risk individuals are
Men >45 and women>55
Those with more than one coronary risk factor
Those with known coronary artery disease
Those experiencing any sign or symptoms.

Important points.

It is important to err on the side of caution. Talk to a Doctor if answered yes on the PAR-Q or have any signs or symptoms of disease or have more than one risk factor.

People who are unfit have greater incidences of exercise related sudden cardiac death and myocardial infarction.

Question why you are starting an exercise program, unfortunately some initiate an exercise program due to having new symptoms. They start to reassure themselves that they are well. These individuals are at risk.

Follow the mantra of start slowly, progress gradually.

Once again understand the signs and symptoms of disease; dyspnea, syncope, chest discomfort. Seek medical evaluation if present.

It's utmost importance to discuss with a physician the effects of medications. Some may affect heart rate and blood pressure during exercise.

Before starting you'll need to learn how to judge your level of exercise exertion and measure heart rate and . These techniques will be valuable in your training program as well as.

See RPE and measuring heart rate questions?