Depolarization and relaxation are two distinct but related processes in the context of the cardiac cycle. Depolarization refers to the initial phase where the heart muscle cells, or cardiomyocytes, lose their resting membrane potential and become excited. This is a result of an influx of positively charged ions, which triggers the heart muscle to contract. The P wave on an ECG represents atrial depolarization, which leads to the contraction of the atria. Relaxation, on the other hand, occurs after contraction and is the phase where the heart muscle returns to its resting state. This is known as repolarization for the electrical activity and diastole for the mechanical activity of the heart. During this phase, the heart muscle cells recover and reset their membrane potential in preparation for the next contraction. To summarize, depolarization is the process that leads to the contraction of the heart muscle, while relaxation is the process that follows contraction, allowing the heart muscle to rest and reset. read more >>

This is the first phase of the cardiac cycle. It is initiated by the P wave of the electrocardiogram (ECG), which represents electrical depolarization of the atria. Atrial depolarization initiates contraction of the atrial musculature.read more >>