Phasic diastolic coronary artery compression (PDCAC) is a rare phenomenon caused by the compression of a coronary artery between expanding myocardium and a non-compliant overlying structure. We report a unique case of an elderly female who presented with recurrent paradoxical substernal chest pain at rest caused by PDCAC of the proximal left circumflex artery (LCx). Her chest pain likely occurred at rest due to longer diastolic compression time at slower heart rates. Pericardial adhesion secondary to past breast radiation was the likely cause of PDCAC. She was treated successfully with oral anti-hypertensive and anti-anginal medical therapy. PDCAC is a rare phenomenon but should be on the differential for chest pain occurring at rest, especially if there is a history of mediastinal or cardiac radiation or inflammation. PDCAC treatment depends on the underlying cause but can be treated successfully with medical therapy alone.