Cardiac tamponade is caused by fluid accumulating in the pericardium, which places pressure on the heart and reduces ventricular filling. It is a medical emergency. The fluid buildup is usually due to malignant diseases, infections like HIV or tuberculosis, trauma, drugs, or other conditions. Symptoms include dyspnea, tachycardia, and muffled heart sounds. Diagnosis involves echocardiogram, which shows collapsed heart structures, and ECG changes. Treatment requires pericardiocentesis to drain fluid along with other supportive measures, followed by treating the underlying cause.