The formation of the cryopyrin inflammasome in the heart induces an intense inflammatory response during acute myocardial infarction (AMI), which mediates further damage and promotes adverse cardiac remodelling. Active interleukin‐1β (IL‐1β) is a key product of the inflammasome, being cleaved by active caspase‐1. The aim of this study was to dissect the role of IL‐1β from that of the inflammasome by using a neutralizing monoclonal antibody directed against IL‐1β and measuring the intensity of the inflammatory response, the activity of caspase‐1 in the inflammasome, cardiomyocyte apoptosis and cardiac remodelling in a mouse model of non‐reperfused AMI. A mouse monoclonal IgG2a antibody directed against IL‐1β (IL‐1β‐AB; 10 mg kg⁻¹) was given i.p. immediately after surgery and repeated 1 week later. Cardiac tissue was analysed at 72 h after surgery in a subgroup of mice for inflammasome aggregates and caspase‐1 activity (inflammasome) and for DNA fragmentation and caspase‐3 activity (apoptosis). All sham‐operated mice were alive at 10 weeks, whereas 40% of the control‐antibody‐treated mice and 30% of the IL‐1β‐AB‐treated mice died during the 4 weeks after surgery. When compared with vehicle, treatment with the IL‐1β‐AB did not affect inflammasome formation or caspase‐1 activation in the heart tissue at 72 h after AMI nor circulating plasma IL‐6 levels, but did inhibit cardiomyocyte apoptosis, limit left ventricular enlargement by 40% (P < 0.01) and improve systolic dysfunction by 17% (P < 0.01) after AMI. These findings suggest that IL‐1β mediates the deleterious effects on the heart during the sterile inflammatory response.