Key points Angiotensin II (AngII) is crucial in cardiovascular regulation in perinatal mammalians. Here we show that AngII increases twitch Ca2+ transients of mouse immature but not mature cardiomyocytes by robustly activating CaV1.2 L‐type Ca2+ channels through a novel signalling pathway involving angiotensin type 1 (AT1) receptors, β‐arrestin2 and casein kinase 2. A β‐arrestin‐biased AT1 receptor agonist, TRV027, was as effective as AngII in activating L‐type Ca2+ channels. Our results help understand the molecular mechanism by which AngII regulates the perinatal circulation and also suggest that β‐arrestin‐biased AT1 receptor agonists may be valuable therapeutics for paediatric heart failure. Abstract Angiotensin II (AngII), the main effector peptide of the renin–angiotensin system, plays important roles in cardiovascular regulation in the perinatal period. Despite the well‐known stimulatory effect of AngII on vascular contraction, little is known about regulation of contraction of the immature heart by AngII. Here we found that AngII significantly increased the peak amplitude of twitch Ca2+ transients by robustly activating L‐type CaV1.2 Ca2+ (CaV1.2) channels in mouse immature but not mature cardiomyocytes. This response to AngII was mediated by AT1 receptors and β‐arrestin2. A β‐arrestin‐biased AT1 receptor agonist was as effective as AngII in activating CaV1.2 channels. Src‐family tyrosine kinases (SFKs) and casein kinase 2α’β (CK2α’β) were sequentially activated when AngII activated CaV1.2 channels. A cyclin‐dependent kinase inhibitor, p27Kip1 (p27), inhibited CK2α’β, and AngII removed this inhibitory effect through phosphorylating tyrosine 88 of p27 via SFKs in cardiomyocytes. In a human embryonic kidney cell line, tsA201 cells, overexpression of CK2α’β but not c‐Src directly activated recombinant CaV1.2 channels composed of C‐terminally truncated α1C, the distal C‐terminus of α1C, β2C and α2δ1 subunits, by phosphorylating threonine 1704 located at the interface between the proximal and the distal C‐terminus of CaV1.2α1C subunits. Co‐immunoprecipitation revealed that CaV1.2 channels, CK2α’β and p27 formed a macromolecular complex. Therefore, stimulation of AT1 receptors by AngII activates CaV1.2 channels through β‐arrestin2 and CK2α’β, thereby probably exerting a positive inotropic effect in the immature heart. Our results also indicated that β‐arrestin‐biased AT1 receptor agonists may be used as valuable therapeutics for paediatric heart failure in the future.