21. For the purposes of this Division, the following functional cardiac classification is established:(1) Class I: no limitation of activity and no symptoms from daily activities;
(2) Class II: slight limitation of activity but comfortable at rest or during mild physical activity;
(3) Class III: marked limitation of activity and comfortable only at rest;
(4) Class IV: the person should be at complete rest, confined to bed or chair and any physical activity brings on discomfort and symptoms may occur even at rest.