Background: Infectious diseases can affect the heart, causing myocarditis, arrhythmias, pericardial effusion, and heart failure. Viral and parasitic infections are major contributors globally, but data from Bangladesh are limited, often from hospitalized patients with short follow-up. This study aims to assess the prevalence, patterns, and risk factors of cardiac manifestations in Bangladeshi patients and evaluate their short- and long-term outcomes to guide better management and prevention. Methods: This cross-sectional study at Zilla Sadar Hospital, Lakhmipur (Jan–Dec 2023) included 125 adults with bacterial, viral, or parasitic infections, excluding those with pre-existing cardiac disease. Sociodemographic, clinical, and laboratory data (troponin, CRP, leukocytosis, anemia) were collected. Cardiac evaluation included ECG and echocardiography for tachycardia, hypotension, arrhythmias, murmurs, heart failure, pericardial effusion, myocarditis, and valvular abnormalities. Data were analyzed using SPSS 25.0 with Chi-square tests (p<0.05). Ethical approval and informed consent were obtained. Results: Among 125 participants (56% male, mostly 31–45 years), viral infections were most common (48%). Cardiac manifestations included tachycardia (54.4%), hypotension (19.2%), heart failure (16.0%), pericardial effusion (14.4%), arrhythmias (12.0%), myocarditis (9.6%), and new murmurs (8.0%). Tachycardia was common across ages and slightly higher in males. Bacterial infections had more hypotension (28.0%) and heart failure (24.0%). Elevated troponin (26.7%), CRP (77.8%), leukocytosis (62.2%), and anemia (40.0%) were significantly associated with cardiac involvement. Conclusion: Cardiac involvement, especially tachycardia, is common in systemic infections and correlates with elevated troponin, CRP, leukocytosis, and anemia. Early ECG, echocardiography, and lab evaluation are essential for detection and management.