The aim of our study was to analyze muscle strength in patients with recent surgical treatment for ischemic and combined ischemic- valvular heart disease, based on existence of diabetes mellitus. Connections existing between muscle strength and patient characteristics or conventional diagnostic tests were analyzed as well. Study prospectively included consecutive patients scheduled for cardiovascular rehabilitation 0–3 months after heart surgery. Diagnostics covered drug utilization, anthropometrics, demographics, echocardiography, conventional laboratory, echocardiography, bioelectrical impedance analysis (BIA), and hand grip test (HGT). HGT was analyzed for dominant hand. Patients with diabetes had significantly weaker muscle strength on HGT than controls ; 29.4 ± 12.2 kg vs. 38.2 ± 14.7 kg (p = 0.029), respectively. ROC analysis for HGT and existence of diabetes mellitus were significant ; ≤ 40 kg had sensitivity of 89.7% (95%CI: 72.6–97.8), specificity 43.7% (31.9– 56.0) ; AUC 0.669 (0.568–0.760) ; p = 0.002. HGT significantly correlated with hematocrit (Rho CC = 0.247 ; p = 0.013), whilst other laboratory or echocardiographic parameters were insignificant (all p > 0.05). HGT also correlated with body weight (Rho CC = 0.510 ; p < 0.001) ; height (Rho CC = 0.632 ; p < 0.001) ; waist circumference (Rho CC = 0.388 ; p < 0.001) ; waist-to-hip ratio (Rho CC = 0.274 ; p = 0.006) and BIA (Rho CC = − 0.412 ; p < 0.001). In postoperative recovery of patients with diabetes, muscle strength assessed by HGT is decreased and in relation with nutritional status. Clinically resourceful connections of HGT were also found to hematocrit and utilization of loop diuretics.