The depression of the ST-segment depicts ischemia.

Explanation:
The ST-segment is a portion of the electrocardiogram (ECG) waveform that represents the period between ventricular depolarization and repolarization. It is the flat, isoelectric line that follows the QRS complex and precedes the T wave. The ST-segment is important in diagnosing various cardiac conditions.

Ischemia:
Ischemia refers to inadequate blood supply to a particular tissue or organ. In the context of the heart, ischemia occurs when there is reduced blood flow to the coronary arteries, which supply oxygen and nutrients to the heart muscle. This can result from a narrowing or blockage in the coronary arteries due to atherosclerosis or a blood clot.

Depression of the ST-segment:
The depression of the ST-segment on an ECG indicates myocardial ischemia. It is typically seen as a downward deflection below the isoelectric line. The degree of ST-segment depression can vary depending on the severity and extent of the ischemia.

Causes of ST-segment depression:
ST-segment depression can be caused by various conditions, including:

1. Coronary artery disease: Atherosclerosis or a blood clot in the coronary arteries can reduce blood flow to the heart muscle, leading to ischemia and ST-segment depression.

2. Angina pectoris: This is chest pain or discomfort that occurs when the heart muscle does not receive enough blood flow. ST-segment depression may be present during an angina episode.

3. Myocardial infarction (heart attack): In a myocardial infarction, there is a complete or partial blockage of a coronary artery, resulting in the death of heart muscle. ST-segment depression may be seen in the early stages of a heart attack.

4. Cardiac ischemia during exercise (stress test): During an exercise stress test, the heart is subjected to increased demand for oxygen. If there is an underlying coronary artery disease, ST-segment depression may occur during exercise due to inadequate blood supply to the heart.

Conclusion:
In summary, the depression of the ST-segment on an ECG indicates myocardial ischemia, which is caused by reduced blood supply to the heart muscle. It can be seen in various conditions such as coronary artery disease, angina, myocardial infarction, and during exercise stress tests. Proper interpretation of the ST-segment changes is crucial in diagnosing and managing cardiac conditions.