Epicardial catheter ablation is necessary to address ventricular tachycardia targets located far from the endocardium, but epicardial adipose tissue and coronary blood vessels can complicate ablation. We demonstrate that catheter-based near-infrared spectroscopy (NIRS) can identify these obstacles to guide ablation. Eighteen human ventricles were mapped ex vivo using NIRS catheters with optical source-detector separations (SDSs) of 0.6 and 0.9 mm. A logistic regression model trained from manually labeled spectra achieved mean area under the receiver operating characteristic curve (AUROC) of 0.907 (0.6 mm SDS) and 0.911 (0.9 mm SDS) in binary adipose detection. Novel optical indices for adipose detection were also proposed, achieving AUROCs of 0.881 (0.6 mm SDS) and 0.873 (0.9 mm SDS), while a blood-specific optical index achieved AUROC of 0.859 for vessel detection (0.9 mm SDS). These results suggest that catheter-based NIRS can detect adipose tissue and coronary vessels to improve efficacy and safety of epicardial ablation.