Anthracyclines are potent cytostatic drugs, the correct dosage being critical to avoid possible cardiac side effects. ABCC1 [ATP-binding cassette, sub-family C, member 1; also denoted as MRP1 (multidrug resistance-associated protein 1)] is expressed in the heart and takes part in the detoxification and protection of cells from the toxic effects of xenobiotics, including anthracyclines. Our objective was to search for associations between LV (left ventricular) function and single-nucleotide polymorphisms of the ABCC1 gene in children receiving anthracycline chemotherapy. Data of 235 paediatric patients with acute lymphoblastic leukaemia was analysed. Patients were followed-up by echocardiography (median follow-up 6.3 years). Nine polymorphisms in the ABCC1 gene were genotyped. The ABCC1 rs3743527TT genotype and rs3743527TT—rs246221TC/TT genotype combination were associated with lower LVFS (left ventricular fractional shortening) after chemotherapy. The results suggest that genetic variants in the ABCC1 gene influence anthracycline-induced LV dysfunction.