Aims: Steroidal mineralocorticoid receptor antagonists (MRAs) form a cornerstone of the management of heart failure (HF), but little is known about the long-term effects of MRA therapy on kidney function. We evaluated acute and chronic estimated glomerular function (eGFR) slopes in the two largest completed trials testing steroidal MRAs in chronic HF. Methods and results: We conducted parallel post hoc eGFR slope analyses in two multinational, double-blind randomized, placebo-controlled trials of steroidal MRAs in chronic HF with reduced ejection fraction (EMPHASIS-HF) and preserved ejection fraction (TOPCAT Americas region). GFR was estimated using the Chronic Kidney Disease Epidemiology Collaboration equation. Annual slopes of eGFR were assessed by generalized random coefficient models. Least square mean differences in eGFR slopes between steroidal MRA and placebo arms were assessed. Median follow-up was 1.8 years (EMPHASIS-HF) and 3.3 years (TOPCAT Americas). From baseline to month 4-6 ('acute eGFR slope'), compared to placebo, MRA treatment led to an acute decline in eGFR of -2.4 ml/min/1.73 m² (95% confidence interval [CI] -3.4 to -1.4; p < 0.001) and -2.0 ml/min/1.73 m² (95% CI -3.0 to -1.8; p < 0.001) in EMPHASIS-HF and TOPCAT Americas, respectively. From month 4-6 to end of study, there was no difference in 'chronic eGFR slope' between MRA and placebo arms (-0.3 ml/min/1.73 m² /year [95% CI -1.3 to 0.7; p = 0.53] and 0.1 ml/min/1.73 m² /year [95% CI -1.4 to 1.7; p = 0.86]) in EMPHASIS-HF and TOPCAT Americas, respectively. Conclusions: Steroidal MRAs result in acute declines in eGFR but do not modify long-term kidney disease trajectories in chronic HF with reduced or preserved ejection fraction.