Structural and functional changes ensue in cardiac cell networks, when cells are guided by 3D scaffold topography. Here, we report enhanced synchronous pacemaking activity in association with slow diastolic rise in intracellular calcium ([Ca²⁺]_i) in cell networks grown on microgrooved scaffolds. Topography-driven changes in cardiac electromechanics were characterized by the frequency dependence of [Ca²⁺]_i in syncytial structures formed of ventricular myocytes, cultured on microgrooved elastic scaffolds (G). Cells were electrically paced at 0.5 to 5Hz, and [Ca²⁺]_i was determined using microscale ratiometric (Fura-2) fluorescence. Compared to flat (F) controls, the G networks exhibited elevated diastolic [Ca²⁺]_i at higher frequencies, increased systolic [Ca²⁺]_i across the entire frequency range, and steeper restitution of calcium transient half-width (n=15 G, 7 F; p<0.02). Significant differences in frequency response of force-related parameters were also found, e.g. overall larger total area under the Ca²⁺ transients, and faster adaptation of relaxation time to pacing rate (p<0.02). Altered [Ca²⁺]_i dynamics was paralleled by higher occurrence of spontaneous calcium release and by increased sarcoplasmic reticulum load (p<0.02), indirectly assessed by caffeine-triggered release. Electromechanical instabilities - calcium and voltage alternans - were more often observed in G samples. Taken together, these findings 1) represent some of the first functional electromechanical data for this in vitro system; and 2) demonstrate direct influence of the microstructure on cardiac function and susceptibility to arrhythmias via calcium-dependent mechanisms. Overall our results substantiate the idea of guiding cellular phenotype by cellular microenvironment, e.g. scaffold design in the context of tissue engineering.