N-cadherin is a cell-surface, Ca(2+)-dependent adhesion molecule found in intercalated disks and extrajunctional sites in the myocardium. In this paper we show that antibodies specific for N-cadherin inhibit the contraction of both interacting and single myocytes isolated from embryonic chicken hearts. Quantitative electron microscopy revealed that anti-N-cadherin significantly decreases cell-cell contact between interacting myocytes, consistent with a role for N-cadherin as a cell-cell adhesion molecule. In addition, quantitative electron microscopy showed that anti-N-cadherin treatment of cardiomyocytes results in a significant reduction in the cytoplasmic area occupied by myofibrils, implying that N-cadherin also plays a role in myofibrillogenesis. We propose that N-cadherin, in addition to mediating cardiac myocyte interaction, promotes myofibril formation necessary for functional activity of the myocardium.