Background: Ca is the most important minerals in the body that plays a key rols in the physiological activities, anzymatic reaction and the regulation of myocardial contraction and relax-ation. Ca deficiency causes the heart failure and decrease cardiac contractility. OBJECTIVES: To determine the effects of long-term dietary calcium deficiency on the heart function of layer hens based on the electro- and echocardiography. METHODS: Ninety Hyline W36 hens were kept for 21 weeks and fed by rations with different amounts of calcium. At 20, 28 and 36 weeks of age, electrocardio-graphic, echocardiographic and post-mortem left ventricular parameters were assessed. RESULTS: S wave amplitude was significantly (p<0.05) increased in the Ca-deficient group II (in lead II) at 36 weeks of age in compared to control. There were also elevations of the QRS wave amplitudes in 28 and 36 weeks of age at two Ca-deficient groups (leads II, III, aVR, aVL and aVF) but were only significant (p<0.05) in Ca-deficient group II (leads II and aVF) in compared to control. Left ventricular free wall diameter at end-systole were significantly (p<0.05) increased in the Ca-deficient group II at 28 and 36 weeks of age compared to the control group. Inter-ventricular septal diameters at end-systole were decreased in two Ca-deficient groups at 28 and 36 weeks (p<0.05). Left ventricular free wall diameter at post-mortem were significant-ly (p<0.05) increased in two Ca-deficient groups at 36 weeks of age compared to the control group. CONCLUSIONS: From these results, it can be suggested that long-term dietary calcium deficiency alters in electro- and echocardiographic parameters, which could reflect pathological left ventricular hypertrophy in the laying hens.