The cardiovascular system exhibits significant daily rhythms in physiologic processes (heart rate, blood pressure, cardiac contractility and function), and molecular gene and protein expression. An increasing number of clinical and experimental studies demonstrate the circadian system is an important underlying mechanism that coordinates these rhythmic processes for the health of the cardiovascular system. However, what happens when rhythms are disturbed has been generally clinically unappreciated. Here we describe the profound adverse impact of disturbed circadian rhythms and sleep on the cardiovascular system, including recovery from myocardial infarction in acute care settings, shift work and heart disease, sleep disorders including obstructive sleep apnea, and cardiovascular pathophysiology associated with disturbed nocturnal blood pressure profiles. We also discuss therapeutic applications of circadian rhythms for the cardiovascular system. Cardiovascular disease is a leading cause of death worldwide, and applying circadian biology to cardiology (and indeed medicine in general) provides a new translational approach to benefit patients clinically.