Background: Aging per se is a risk factor for reduced cardiac function and heart diseases, even when adjusted for aging-associated cardiovascular risk factors. Accordingly, aging-related biochemical and cell-biological changes lead to pathophysiological conditions, especially reduced heart function and heart disease. Objective: In this review, we summarize the changes that occur as the heart ages from youth to old age on the basis of the cardiac myocyte. Aging phenotypes and underlying mechanisms shall be discussed that affect cardiomyocyte repair, signaling, structure, and function. Methods: Review of the literature. Results: The following factors play vital roles in the aging of cardiomyocytes: oxidative stress, inflammation, cellular protection and repair, telomere integrity, survival and death, metabolism, post-translational modifications, and altered gene expression. Importantly, non-cardiomyocyte-based aging processes (vascular, fibroblast, extracellular matrix, etc.) in the heart will interfere with cardiomyocyte aging and cardiac function. Conclusion: Based on our analyses, we postulate that the physiological aging process of the heart and of the cardiomyocyte is primarily driven by intrinsic aging factors. However, extrinsic aging factors, e.g. smoking, also make an important contribution to pathologically accelerated aging of the heart.