A 48-year-old woman presented with progressive exertional dyspnoea, orthopnoea and weight gain. Physical examination revealed bilateral rales, a third heart sound, a holosystolic murmur over the apex, abdominal and peripheral oedema.

Electrocardiogram showed left bundle branch block (Fig. 1 panel a). Heart size was markedly increased on chest X‑ray (Fig. 1 panel b). On transthoracic echocardiography left ventricular ejection fraction was severely depressed (LVEF 16%; video 1) with severe secondary mitral regurgitation. This was corroborated by cardiac magnetic resonance imaging (LVEF 18%). Coronary artery disease was excluded on coronary computed tomography. The patient was diagnosed with dilated cardiomyopathy and treated with optimal medical therapy.

Fig. 1
figure 1

Electrocardiogram and chest X‑ray before (panel a and panel b) and after (panel c and d) cardiac resynchronisation therapy

Full size image

Cardiac resynchronisation therapy was initiated under which QRS duration decreased significantly (Fig. 1 panel c), as well as a marked reduction in heart size on chest X‑ray and transthoracic echocardiography (Fig. 1 panel d; video 2). The patient rapidly recovered and shows no signs or symptoms of heart failure.