This book summarizes our current understanding about the biology and patho-biology of cardiomyocytes and depicts common techniques for the study of these cells. The book is divided into two parts; the first part provides insight into role and function of cardiomyocytes under normal conditions and describes embryogenesis and differentiation, in the second part the role of cardiomyocytes in aging and disease is discussed and cellular responses under stress conditions illustrated. Cardiomyocytes represent the main mass of the heart, and cellular malfunction directly modifies heart function leading to subsequent heart failure.