The ratio of early transmitral filling velocity to early diastolic strain rate (E/SRe) has been proposed as a new non-invasive measurement of left ventricular filling pressure. We aimed to investigate the ability of E/SRe to predict atrial fibrillation (AF) after ST-elevation myocardial infarction (STEMI). This was a prospective cohort study of patients (n = 369) with STEMI. Patients underwent an echocardiographic examination a median of two days after pPCI. By echocardiography, transmitral early filling velocity (E) was measured by pulsed-wave Doppler, and early diastolic strain rate (SRe) was measured by speckle tracking of the left ventricle. E was indexed to SRe and the early myocardial relaxation velocity (e’) to obtain the E/SRe and E/e’, respectively. The endpoint was new-onset AF. During follow-up (median 5.6 years, IQR: 5.0–6.1 years), 23 (6%) of the 369 patients developed AF. In unadjusted analyses, both E/SRe and E/e’ were significantly associated with AF [E/SRe: HR = 1.06; (1.03–1.10); p < 0.001, per 10 increase] and [E/e’: HR = 1.11 (1.05–1.17); p < 0.001, per 1 increase] and had equal Harrell’s C-statistic of 0.71. However, only E/SRe remained an independent predictor after multivariable adjustments for clinical and echocardiographic parameters [E/SRe: HR = 1.06 (1.00–1.11); p = 0.044, per 10 increase]. E/SRe was further significantly associated with AF in patients with E/e’ < 14 HR = 1.09 (1.01–1.17); p = 0.030, per 10 increase), also after multivariable adjustments. E/SRe is an independent predictor of AF in STEMI patients, even in subjects with seemingly normal filling pressure.