I have warned about people who make New year resolutions to exercise but, in case you are one of those who do so, do me a favor and get a Stress Echo first if you are a male over 40 or in bad shape over 30, a post-menopausal woman, or anybody who fatigues with either extended activity or exertion.
A Stress Echo not only can identify heart issues before they appear in daily life, but can give you a metabolic physical stress tolerance baseline. Most Stress Echo protocols push you to your max unless you have prior identified cardio-pulmonary disease, so the attending cardiologist will be able to give you a thorough cardio fitness assessment and a numerical metabolic fitness level. (This test is required regularly for firemen, pilots, athletes, etc.) Serious fitness trainers also want an OK before pushing their clients hard.