What are the rules for training the heart muscle?

Basically, various exercises for training the heart muscle are very dangerous to health and have a negative effect. Many people believe that running, swimming and other endurance exercises can make the heart stronger. In fact, it is very harmful to health. The heart muscle should work stably and if there is no doctor’s recommendation, it is better not to overload the heart so that heart diseases do not develop. To make the heart more stable, you need to start with light endurance exercises, gradually increasing the load.