Background. Mutations in ATP1A2 gene encoding the Na,K-ATPase α2 isoform is associated with familial hemiplegic migraine type 2 (FHM2). Migraine with aura is a known risk factor for heart disease. The Na,K-ATPase is important for cardiac function but its role for heart disease remains unknown. We hypothesized that ATP1A2 is a susceptibility gene for heart disease and aimed to assess the underlying disease mechanism. Methods and Results. Mice heterozygous for the FHM2-associated G301R mutation in the Atp1a2 gene (α2+/G301R mice) and matching wild type (WT) controls were compared. Reduced expression of the Na,K-ATPase α2 isoform and increased expression of the α1 isoform was observed in hearts from α2+/G301R mice (Western blot). Left ventricular dilation and reduced ejection fraction was shown in hearts from 8-month-old α2+/G301R mice (cardiac magnetic resonance imaging) and this was associated with reduced nocturnal blood pressure (radiotelemetry). Cardiac function and blood pressure of 3-month-old α2+/G301R mice were similar to WT mice. Amplified Na,K-ATPase-dependent Src/Ras/Erk1/2 signaling was observed in hearts from 8-month-old α2+/G301R mice and this was associated with mitochondrial uncoupling (respirometry), increased oxidative stress (malonedialdehyde measurements), and a heart failure-associated metabolic shift (hyperpolarized magnetic resonance). Mitochondrial membrane potential was similar between the groups (JC-1 dye assay). Proteomics of heart tissue further suggested amplified Src/Ras/Erk1/2 signaling and increased oxidative stress and provided the molecular basis for systolic dysfunction in 8-month-old α2+/G301R mice. Conclusions. Our findings suggest that ATP1A2 mutation leads to disturbed cardiac metabolism and reduced cardiac function mediated via Na,K-ATPase-dependent ROS signaling through the Src/Ras/Erk1/2 pathway.