Mutations in the AARS2 gene are linked to infantile cardiomyopathy; however, the underlying molecular mechanism remains unknown. Here, we report that PCBP1, a poly(rC) binding protein, interacts with the AARS2 transcript to mediate its alternative splicing. Cardiomyocyte-specific deletion of Pcbp1 in mice impairs normal splicing and causes premature termination of Aars2, leading to defects in heart development and postnatal lethality. Similarly, mice with a deletion in Aars2 that mimics a disease-causing splicing lesion display heart developmental abnormalities, reminiscent of those in patients with infantile mitochondrial cardiomyopathy. Mechanistically, loss of Pcbp1 or Aars2 in the heart reduces oxidative phosphorylation, a hallmark of patients with AARS2 mutations. This reduction in mitochondrial-encoded proteome activates mitonuclear communication and the UPR pathway, thereby inducing a compensatory nuclear-encoded mitochondrial gene program. Our findings provide insights into the PCBP1-AARS2 regulatory axis in mitochondrial cardiomyopathy.