The major findings were: (a) blunted positive inotropic response to isoproterenol and elevated [Ca2+]o; (b) healthy‐like positive chronotropic response in DMD cardiomyocytes; (c) depressed SR Ca2+ release in DMD cardiomyocytes, likely to underlie the attenuated positive inotropic response; (d) RNA‐expression levels of specific subunits of the L‐type calcium channel, β1‐adrenergic receptor (ADRβ1) and adenylate cyclase are down‐regulated in DMD cardiomyocytes, which collectively may contribute to the depressed β‐adrenergic inotropic responsiveness. Here, ADCY1 is linked to Duchenne muscular dystrophy.