It must be because of the history of heart surgery that I dare not use force and the intensity is low. But you don't have to force your heart to beat fast, and the purpose of exercise is achieved. The important thing is that your breathing and heartbeat are harmonious when you run. You may not feel it, but it is also good for your heart.
Now, for you, exercise should be as gradual as possible. As for running, the emphasis is persistence and perseverance. You will find that running is a good way to keep fit and is good for your health.
May you be healthy forever! ! ! !