Myocardial infarction (MI) results from sudden atherothrombotic occlusion of a coronary artery, exhibits a genetic predisposition and clusters in families. We performed whole exome sequencing and analysed identified targets. In a MI family, heterozygous mutations in two functionally related genes, GUCY1A3, encoding the a₁-subunit of the soluble guanylyl cyclase (a₁-sGC), and CCT7, encoding a chaperonin containing TCP-1 complex (CCT) protein, segregate with the disease. All family members with the GUCY1A3 (p.Leu163Phefs*24) and the CCT7 mutation (p.Ser525Leu) were affected. Transfection of sGC in HEK cells yielded its expression and NO-induced cGMP formation, but transfection of the GUCY1A3 mutation was ineffective. Downregulation of CCT7 in VSM decreased sGC expression verifying the importance of CCT7 herein. In platelets of affected probands a₁-sGC and NO-induced cGMP formation was strongly reduced. Light-dye induced thrombus formation in arterioles revealed the functional relevance of a₁-sGC. Time to occlusion was shorter in a₁-sGC deficient mice. Inhibition of endogenous NO accelerated thrombus formation only in wildtype and abrogated differences between genotypes indicating an absent inhibitory effect of NO in a₁-sGC-/- mice. In conclusion, dysfunctional NO/sGC signalling may lead to premature MI and a₁-sGC is decisive in continuous inhibition of thrombus formation thereby preventing MI.