Timely use of Sacubitril/Valsartan has the potential to significantly improve cardiac function and dramatically reduce secondary mitral regurgitation (MR) severity even in patients presenting with acute decompensated heart failure (HF), not only in compensated chronic HF patients. The outstanding impact of echocardiography is obvious in monitoring improvement of cardiac function and MR severity in patients with heart failure with reduced ejection fraction (HFrEF). We report a relevant case of an elderly patient who presented with acute decompensated HF with severe bi-ventricular dysfunction and severe MR. He was previously on optimal medical therapy (OMT), however still symptomatic. Coronary angiogram (CAG) depicted three vessel coronary artery disease (CAD). Patient advised to undergo coronary artery bypass graft surgery (CABG) with mitral valve repair, then followed by implantation of a cardiac resynchronization therapy defibrillator device (CRT-D) if no LV function improvement observed after revascularization. Patient’s ECG showed a QRSd ≥ 125 ms, hence a good candidate for CRT. Two weeks after starting Sacubitril/Valsartan the LV EF improved from 15% to 40%. Severe MR reduced to grade II and there was dramatic improvement of patient’s symptoms from NYHA class IV to NYHA class I. NT-proBNP reduced from 9,000 pg/ml to 800 pg/ml. Following an elective percutaneous coronary intervention (PCI), LV EF further improved to 50%. The patient was symptoms-free with preserved LV EF on follow up for 18 months later. This case report documents the swift echocardiographic and symptom improvement in an elderly patient with decompensated end-stage HF when Sacubitril/Valsartan started during the acute setting