Inclusion Criteria:  Age ≥ 18 years Eastern Cooperative Oncology Group (ECOG) performance status ≤ 2 (Karnofsky ≥ 60%)  Patients must have histologically confirmed recurrent or metastatic urothelial carcinoma (renal pelvis, ureter, bladder, or urethra), planned for treatment with pembrolizumab under an Food and Drug Administration (FDA) approved indication (listed below) at the genitourinary oncology clinics of Emory University's Winship Cancer Institute:  First line: locally advanced or metastatic urothelial carcinoma who are not eligible for cisplatin-containing chemotherapy and whose tumors express PD-L1 (Combined Positive Score [CPS] ≥ 10) as determined by an FDA-approved test, or in patients who are not eligible for any platinum-containing chemotherapy regardless of PD-L1 status Second line: locally advanced or metastatic urothelial carcinoma after progression on platinum-based chemotherapy Patients must have measurable disease as defined by RECIST criteria as at least one lesion that can be accurately measured in at least one dimension (longest diameter to be recorded as ≥ 10 mm (≥ 1 cm) on computed tomography (CT) scan or magnetic resonance imaging (MRI) Patients must have adequate organ and marrow function, within 28 days of cycle 1 day 1, at the discretion of the investigator The effects of study drugs on the developing human fetus are unknown. For this reason, female of child-bearing potential (FCBP) must have a negative serum or urine pregnancy test prior to starting therapy  FCBP and men treated or enrolled on this protocol must agree to use adequate contraception (hormonal or barrier method of birth control; abstinence) prior to study entry, for the duration of study participation, and 3 months after completion of study drug administration. Should a woman become pregnant or suspect she is pregnant while she or her partner is participating in this study, she should inform her treating physician immediately.  A female of childbearing potential (FCBP) is a sexually mature woman who: 1) has not undergone a hysterectomy or bilateral oophorectomy; or 2) has not been naturally postmenopausal for at least 24 consecutive months (i.e., has had menses at any time in the preceding 24 consecutive months) Completion of all previous therapy (including surgery, radiotherapy, chemotherapy, immunotherapy, or investigational therapy) for the treatment of cancer ≥ 4 weeks before the start of study therapy  Patients with known history or current symptoms of cardiac disease, or history of treatment with cardiotoxic agents, should have a clinical risk assessment of cardiac function using the New York Heart Association Functional Classification. To be eligible for this trial, patients should be class IIB or better  Patients without existing cardiac disease that raise the risk of complications who consent for the trial will proceed with trial participation Patients with existing cardiac disease that could raise the risk of complications will be referred at the discretion of the investigator to a cardio-oncologist who is a co-investigator on the trial (or general cardiologist) for cardiac optimization prior to starting propranolol Life expectancy > 12 weeks as determined by the investigator Willingness and ability of the subject to comply with scheduled visits, drug administration plan, protocol-specified laboratory tests, other study procedures, and study restrictions Evidence of a personally signed informed consent indicating that the subject is aware of the neoplastic nature of the disease and has been informed of the procedures to be followed, the experimental nature of the therapy, alternatives, potential risks and discomforts, potential benefits, and other pertinent aspects of study participation  Exclusion Criteria:  Patients who have had chemotherapy or radiotherapy within 4 weeks prior to entering the study or those who have not recovered from adverse events due to agents administered more than 4 weeks earlier (i.e., have residual toxicities > grade 1) Patients who are receiving any other investigational agents or an investigational device within 21 days before administration of first dose of study drugs History of allergic reactions attributed to compounds of similar chemical or biologic composition to the agents used in study Contraindication to pembrolizumab per investigator discretion Uncontrolled current illness including, but not limited to, ongoing or active infection, symptomatic congestive heart failure, unstable angina pectoris, cardiac arrhythmia, or psychiatric illness/social situations that would limit compliance with study requirements Significant cardiovascular disease (e.g., myocardial infarction, arterial thromboembolism, cerebrovascular thromboembolism) within 3 months prior to start of study therapy; angina requiring therapy; symptomatic peripheral vascular disease; New York Heart Association class 3 or 4 congestive heart failure; or uncontrolled grade ≥ 3 hypertension (diastolic blood pressure ≥ 100 mmHg or systolic blood pressure ≥ 160 mmHg) despite antihypertensive therapy Contraindication to a beta blocker: cardiac conditions that significantly raise the risk of cardiopulmonary complications, including unstable angina, uncontrolled heart failure, symptomatic bradycardia, and severe asthma Current use of an oral or intravenous beta blocker (e.g. atenolol, bisoprolol, carvedilol, labetalol, metoprolol, nadolol, sotalol, among other beta blockers) with inability to safely switch to a non-beta blocker agent. The washout for current users should be at least 14 days with enough transition period