Abstract Body (Do not enter title and authors here): Background:
Acute cardiac tamponade occurs when rising intrapericardial pressure compresses the heart, most commonly affecting right-sided chambers. However, in postoperative or malignant settings, pericardial adhesions or loculated effusions may produce regional tamponade, a variant where localized pressure causes isolated chamber compression. Left ventricular (LV) diastolic collapse, though rare, is a hallmark of this phenomenon when localized intrapericardial pressure exceeds LV diastolic pressure.

Case Presentation:
A 63-year-old man with metastatic EGFR-positive non–small-cell lung cancer and recent pulmonary embolism on rivaroxaban was admitted following elective pleural-peritoneal shunt placement for recurrent malignant pleural effusions. Transthoracic echocardiography (TTE) was notable for a small pericardial effusion on post-operative day 1. On post-operative day 2, he developed hypotension (BP 86/56 mmHg), tachycardia (HR 115 bpm), and elevated lactate (2.9 mmol/L; normal range 0.5 – 2.0 mmol/L). Exam revealed distant heart sounds and jugular venous distension. Repeat TTE demonstrated a large, loculated pericardial effusion with diastolic collapse of the lateral and apical LV (Figure 1), right ventricle, and atria, along with respirophasic mitral/tricuspid inflow variation and expiratory hepatic vein flow reversal. Emergent subxiphoid surgical pericardial window revealed dense adhesions and evacuated 500cc bloody effusion, with immediate hemodynamic improvement. Histopathology confirmed malignant pericardial involvement with clusters of malignant adenocarcinoma cells (Figure 2).

Discussion:
Here we highlight a visually compelling example of tamponade with LV diastolic collapse secondary to a loculated malignant pericardial effusion. LV diastolic collapse is a hallmark sign of regional cardiac tamponade, especially in malignancy or postsurgical states. Prior studies utilizing canine models of regional cardiac tamponade demonstrated that LV diastolic collapse correlated with significant reductions in cardiac output and mean arterial pressure prior to decompensated tamponade. Early recognition of regional tamponade and hallmark signs including LV diastolic collapse is critical to guide interventions and avoid hemodynamic deterioration.