No. As handsonanatomist mentions it has to do with blood flow to the myocardium(heart muscle itself). The heart muscle itself only receives oxygen during diastole(relaxation), but as heart rate increases the relative length of diastole shortens compared to systole(heart contraction). TLDR; your heart gets tired because it only gets oxygen while relaxed, and the relative amount of time spent relaxing is less.
Mind vs Brain. Though mind and brain are two terms that are understood to mean the same when used in the colloquial sense, there is a difference between mind and brain. There is certainly some difference between the two in their making. Brain is made of physical matter while mind is not made of physical matter. To be more elaborate brain is made up of cells, blood vessels and nerves to name a few. Mind is nothing but the thought that resides in the brain.
Difference Between Author and Writer. We often use the words author and writer interchangeably. But indeed both these words are quite different. A writer is a person who writes a book, article, or any literary piece, while an author is essentially the person who originates the idea, plot, or content of the work being written. At times, the author and writer can be the same person. In case of an autobiography, a person writes about the own life.