Androgens are steroid hormones. Testosterone, androstenedione, dehydroepiandrosterone (DHEA), and dehydroepiandrosterone sulfate are the main human androgens. Testosterone has a central role in the maintenance of physiological processes in men. The testosterone synthesis is regulated by the Hypothalamic-Pituitary-Gonadal (HPG) axis. Several male biological processes are regulated by the HPG axis including phenotypic gender development, sexual maturation, and testicular function. Testosterone is metabolized into active metabolites: dihydrotestosterone (DHT) via 5α-reductase, and into estradiol via aromatization. DHT is a much more potent androgen than testosterone owing to the high affinity for the androgen receptor (AR). Several studies on cells, animals, and humans have investigated the effects of testosterone on various organs and metabolism. Recent evidence has demonstrated that androgens regulate vascular tone, improve erythropoiesis, and modulate platelet activities (thrombosis) and cardiac cells electrophysiology and contractile functions. This chapter will discuss testosterone metabolism and the role of testosterone in the cardiovascular system.