As a medical professional with expertise in cardiology, I can tell you that the J point on an ECG is a critical point that marks the end of the depolarization phase and the beginning of the repolarization phase of the cardiac cycle. It is the point where the QRS complex transitions into the ST segment. The J point is significant because any elevation or depression of the ST segment from this baseline can be indicative of various cardiac conditions, such as ischemia or injury. Here's the information structured as requested: English Answer: The J point on an ECG is the precise point at which the QRS complex ends and the ST segment begins. It signifies the transition from the depolarization phase to the repolarization phase of the heart's electrical activity. The J point is located at the junction of the S wave (if present) and the ST segment. It is a critical reference point for assessing changes in the ST segment, which can be indicative of cardiac conditions such as ischemia. 中文回答： 心电图上的J点是QRS波群结束和ST段开始的确切点。它标志着心脏电活动从去极化阶段过渡到复极化阶段。J点位于S波（如果存在）和ST段的交界处。它是评估ST段变化的关键参考点，ST段的变化可能是心脏状况如缺血的指标。 read more >>

On the ECG, the repolarization phase starts at the junction, or j point, and continues until the T wave. The ST segment is normally at or near the baseline. Minor STT changes are not necessarily associated with cardiac ischemia[1]. The T wave is usually concordant with the QRS complex.read more >>